Gross Morphological and Sex Wise Morphometrical Studies on Mandible of Adult Blue Bull (Boselaphus tragocamelus)

The Blue bull (Boselaphus tragocamelus) is regarded as one of the biggest antelopes in Asia and is widely found in both the forests and adjoining villages with enough green grass (Sathapathy et al., 2017, Sathapathy et al., 2018a and Sathapathy et al., 2018b). It belongs to the family Bovidae and comes under the genus Boselaphus (href="#sathapathy_2018">Sathapathy et al., 2018c, Sathapathy et al., 2018d and Sathapathy et al., 2018e). The Blue bull is quite prevalent in northern and central parts of India especially in the foot hills of Himalayas, eastern part of Pakistan and southern part of Nepal, but has vanished from Bangladesh (Sathapathy et al., 2019a, Sathapathy et al., 2019b and Sathapathy et al., 2019c). The adult male of the Blue bull appears like ox and so called as Blue bull (Sathapathy et al., 2019d and Sathapathy et al., 2019e). They are generally seen in day times in the meadow pasture, timberland areas and agricultural land area (Sathapathy et al., 2019f and Sathapathy et al., 2019h). The Blue bulls are safeguarded beneath the IUCN since 2003 and also under safeguard of ‘Schedule III’ of the Indian Wildlife Protection Act, 1972 (Bagchi et al., 2004). The massive body of this animal can be attributed to the large skeleton of the antelope (Sathapathy et al., 2019i and Sathapathy et al., 2019j). Further, the skeleton of the Blue bull comprises of large and massive bones of axial and appendicular skeleton that not only protects the viscera, but also provides shape and support to the heavy musculature (Sathapathy et al., 2020a, Sathapathy et al., 2020b and Sathapathy et al., 2020c). The present study developed a baseline data on the gross morphology and sex wise morphometrical differences in the mandible of adult Blue bull that would immensely help the wild life anatomists and Veterinarians in species identification and solving forensic and vetero-legal cases as no previous work has been done in this field on the Blue bull.

The present study was carried out on the mandible of six specimens of adult Blue bulls (Boselaphus tragocamelus) of either sex. The permission for the collection of mandible bones was acquired from the Principal Chief Conservator of Forests (PCCF), Government of Rajasthan in January, 2015. The skeletons were taken out from the burial ground that was located in the premises of the office of the Deputy Conservator of Forest Wildlife (WL), Jodhpur. After wards, the specimens were boiled in an aluminium vat for about one hour. They were taken out from the vat and air dried for 3-5 days (Choudhary et al., 2013). The morphometrical study was conducted under the supervision of the Zoo Authority, Jodhpur, India. The different biometrical parameters of mandible were measured and subjected to routine statistical analysis as per standard technique given by Snedecor and Cochran (1994) and independent samples t-Test with Systat Software Inc, USA and SPSS 16.0 version software.

The mandible of Blue bull consisted of two rami, i.e. horizontal and vertical rami. The two halves of this bone fused incompletely at the mandibular symphysis, at the midline, which contradictory to the findings of Getty et al., (1930) in horse, where the two halves of the mandible were completely fused. The horizontal ramus further comprised of anterior incisive part and posterior molar part, which was similar to the findings of Getty et al., (1930) in cattle and Dyce et al., (2006) in dog. The lingual surface of incisive part was concave and its labial surface was convex. The alveolar boarder presented eight alveoli for incisor teeth and six sockets for the lower cheek teeth. The ventral boarder was thick. Mental foramen was located at the cranial aspect of the lateral surface of horizontal ramus of mandible (Fig 1) and it was the exterior opening of the mandibular canal, which was similar to the findings of Grossman (1960) in camel and Frandson and Spurgeon (1992) in cattle. The mental foramen is located 4.2±0.12 cm from the rostral most part of mandible in females, whereas it was recorded as 5.1±0.15 cm in male Blue bull. The average distance between the mental foramen and the dorsal boarder of horizontal ramus was found to be 0.9±0.002 cm in both female and male Blue bull. Similarly, the average distance between the mental foramen and the ventral boarder of horizontal ramus was found to be 2.1±0.04 cm in female and 2.5±0.06 cm male Blue bull respectively.
 

 

       
The vertical ramus extended from the horizontal part and comprised of two boarders, two surfaces and two ends. The ventral end was continuous with the horizontal ramus. The dorsal end has a condylar process and a coronoid process. The condylar process was located behind the coronoid process. The depression between these two processes was known as mandibular notch and the constriction below the notch was called as neck of the mandible, which was similar to the findings of Getty et al., (1930) in cattle, sheep, goat and Sebastiani and Fishbeck (2005) in cattle. The medial surface was slightly concave and presented mandibular foramen and a groove (Fig 2). This foramen was the interior opening of the mandibular canal. The average distance between the mandibular foramen and cranial boarder of vertical ramus was found to be 2.6±0.10 cm in females, whereas it was recorded as 2.2±0.07 cm in male Blue bull. Further, average distance between the mandibular foramen and ventral boarder of vertical ramus was found to be 7.2±0.18 cm in females, whereas it was recorded as 7.3±0.20 cm in male Blue bull. A faint notch was located at the ventral aspect of horizontal ramus just infront of the angle of the jaw.
 

 

 
Biometrical observations
 
The biometrical observations of mandible of Blue bull revealed characteristic differences between the sexes. The average length of horizontal ramus of mandible was found to be 24.7±1.02 cm in female, which was significantly less (P<0.05) than that of males, where it was recorded as 35.4±1.97 cm. The average thickness of horizontal ramus at the caudal aspect was found to be 2.03±0.06 cm in female, which was significantly more (P<0.05) than that of males, where it was recorded as 1.53±0.05 cm. The average width of horizontal ramus at the caudal aspect was found to be 5.9±0.08 cm in female, which was significantly more (P<0.05) than that of males, where it was recorded as 5.5±0.09 cm. The average thickness of vertical ramus at the base was found to be 0.53±0.001 cm in female, which was significantly less (P<0.05) than that of males, where it was recorded as 0.80±0.002 cm. Similarly, the average width of vertical ramus at the base was found to be 6.7±0.16 cm in female, which was significantly less (P<0.05) than that of males, where it was recorded as 8.6±0.09 cm.
       
The average width of vertical ramus at the middle was found to be 4.9±0.11 cm in female, which was significantly less (P<0.05) than that of males, where it was recorded as 6.8±0.10 cm. The average distance between the two horizontal rami at the cranial aspect was found to be 5.4±0.09 cm in female, which was significantly less (P<0.05) than that of males, where it was recorded as 6.9±0.07 cm. Similarly, the average distance between the two horizontal rami at the middle was found to be 7.2±0.13 cm in female, which was significantly less (P<0.05) than that of males, where it was recorded as 8.2±0.17 cm. The average distance between the two horizontal rami at the caudal aspect was found to be 9.1±0.15 cm in female, which was significantly less (P<0.05) than that of males, where it was recorded as 10.2±0.08 cm.
       
The average distance between the two caudal boarders of vertical rami at the apex was found to be 12.3±0.09 cm in female, which was significantly less (P<0.05) than that of males, where it was recorded as 14.2±0.04 cm. Similarly, the average distance between the two caudal boarders of vertical rami at the middle was found to be 11.2±0.16 cm in female, which was significantly less (P<0.05) than that of males, where it was recorded as 13.1±0.08 cm. The average distance between the two caudal boarders of vertical rami at the base was found to be 8.7±0.16 cm in female, which was significantly less (P<0.05) than that of males, where it was recorded as 10.6±0.21 cm.
       
The average cranio-caudal length of mandibular notch was found to be 1.32±0.01 cm in female, which was significantly less (P<0.05) than that of males, where it was recorded as 1.44±0.02 cm. Similarly, the average dorso-ventral depth of mandibular notch was found to be 0.96±0.03 cm in female, which was significantly less (P<0.05) than that of males, where it was recorded as 1.18±0.01 cm. The average diameter of mental foramen was found to be 0.92±0.01 cm in female, which was significantly more (P<0.05) than that of males, where it was recorded as 0.76±0.01 cm. Similarly, the average diameter of mandibular foramen was found to be 0.16±0.01 cm in female, which was significantly less (P<0.05) than that of males, where it was recorded as 0.33±0.01 cm.
       
The average thickness of coronoid process at the apex was found to be 0.26±0.01 cm in female, which was significantly less (P<0.05) than that of males, where it was recorded as 0.36±0.01 cm. Similarly, the average thickness of coronoid process at the middle was found to be 0.39±0.01 cm in female, which was significantly less (P<0.05) than that of males, where it was recorded as 0.48±0.02 cm. The average length of condylar process was found to be 1.8±0.05 cm in female, which was significantly less (P<0.05) than that of males, where it was recorded as 2.6±0.07 cm.
       
The average distance between the two coronoid processes at the apex was found to be 12.0±0.17 cm in female, which was significantly less (P<0.05) than that of males, where it was recorded as 19.5±0.20 cm. Similarly, average distance between the two coronoid processes at the middle was found to be 15.5±0.12 cm in female, which was significantly less (P<0.05) than that of males, where it was recorded as 22.1±0.19 cm. The average distance between the two coronoid processes at the base was found to be 16.1±0.08 cm in female, which was significantly less (P<0.05) than that of males, where it was recorded as 23.9±0.11 cm.
       
The average distance between the two condylar processes at the apex was found to be 12.3±0.07 cm in female, which was significantly less (P<0.05) than that of males, where it was recorded as 14.2±0.13 cm. Similarly, average distance between the two condylar processes at the middle was found to be 11.2±0.12 cm in female, which was significantly less (P<0.05) than that of males, where it was recorded as 13.1±0.16 cm. The average distance between the two condylar processes at the base was found to be 8.7±0.23 cm in female, which was significantly less (P<0.05) than that of males, where it was recorded as 10.6±0.27 cm. 

The mandible of Blue bull consisted of two rami, i.e. horizontal and vertical rami. The two halves of this bone fused incompletely at the mandibular symphysis, at the midline. The various parameters of mandible like the average length, width and thickness of horizontal ramus, the average width and thickness of vertical ramus, the average length and depth of mandibular notch, the average diameters of mental and mandibular foramina, the average length of condylar process, the average thickness of coronoid process, etc. showed characteristic sexual variations. We therefore believe that the data presented above would form a baseline for further work especially comparability and compatibility are now desirable traits as efforts are geared up towards massive improvement in the livestock sector of the international economy.

The authors are grateful to the Ministry of Environment of Forests (MoEF), New Delhi and Jodhpur Zoo, Rajasthan, India for providing facilities and support for carrying out research on the skull bones of Blue bull. Funding was provided by Department of Science and Technology, New Delhi and Indian Council of Agricultural Research, New Delhi, India as Ph.D. grant (DST-INSPIRE Fellowship and ICAR-SRF (PGS) to the first author.