The scapula from the skeleton of an adult monkey died of electric shock was collected from the Veterinary Clinical Complex, DUVASU, Mathura. The scapulae of monkey were irregularly triangular shape flat bone with three borders, three angles and two surfaces. The vertebral border was slanting and continued with the cranial border. The later was thin and convex in its proximal 1/3rd part and concave distally. The caudal border was thin in its initial part but became thick and grooved, distally. The scapular spine divided the lateral surface of scapula into two unequal fossae viz; supraspinous and infraspinous fossa in the ratio of 1:2. The scapular spine started from the vertebral border, ran cranioventral and became more prominent and prolonged distally to form a pointed acromion process. The acromion process was directed craniad and overhung the glenoid cavity. The subscapular fossa formed the costal surface and was marked by several muscular lines. The neck was strong and constricted. The glenoid cavity was elongated oval in shape and continued on to the tuber scapulae. The coracoid process appeared as a well developed hook like projection from the medial aspect of tuber scapulae. These specializations have been discussed in light of their functionality in the monkeys.
The rhesus monkey (Macaca mulatta) is one of the best-known species of old world monkeys. They belong to order primates, family cercopithecidae, genus Macaca and species mulatta. These are native to Northern India, Bangladesh, Pakistan, Nepal, Burma, Thailand, Vietnam, Southern China, and some neighboring areas. The scapula is a thin, flat bone that serves as the bony attachment site for numerous muscles between the head, neck and forelimb of primates (Ashton & Oxnard, 1963). The overall mobility of the forelimb depends to a considerable degree on structure and function of the shoulder region. The paucity of the anatomical description of this bone prompted the authors to put on record their observations.
Materials and Methods
The carcass of an adult monkey died due to electric shock procured from the mortuary of the Veterinary Clinical Complex, DUVASU, Mathura, brought to the Department of Anatomy, macerated and cleaned to prepare the skeleton. The morphology of the scapulae of either side was noted and biometry recorded with the help of digital Vernier Callipers and non-stretchable thread. The biometrical parameters of scapulae of either side were taken and their mean values have been calculated and the results were discussed.
Results and Discussion
The biometrical data of right and left scapulae and their mean values are summerized in Table1.
Table 1: Morphometrical parameters of scapula of monkey
|S. No.||Parameters||Left scapula (mm)||Right scapula (mm)||Mean (mm)|
|3.||Height of scapular spine|
|4.||Thickness of scapular spine|
|5.||Length of acromian process||26||26||26|
|6.||Distance between glenoid cavity and acromian process||17||16||16.5|
|7.||Distance between the rim of glenoid cavity and distal end of acromian process||80||70||75|
|8.||Thickness of cranial border|
|9.||Thickness of caudal border|
|10.||Thickness of vertebral border|
|11.||Thickness of neck of scapula||21.91||21.73||21.82|
|12.||Length of glenoid cavity||17||16||16.5|
|13.||Width of glenoid cavity||11||11||11|
|14.||Length of coracoid process||15||14||14.5|
The scapula was a flat bone which was situated on the cranial part of the lateral wall of the thorax as has been described by Preuschoft et al. (2010) in primates. According to Chan (2007) the arboreal monkeys have more dorsally situated scapula than the terrestrial ones and has also been supported by Preuschoft et al. (2010) in arboreal monkeys. The latter author stated that, the scapula assumed a more dorsal position on wider and less deep thorax of these monkeys. The scapula was roughly triangular in shape with a maximum length and width of 94.5 and 70.5 mm, respectively. The scapular index was 74 % indicating that the scapula had a tendency of being much wider than its length. According to Schmidt et al. (2002) and Schmidt (2001), the length of scapula contributes considerably to step length because of its rotation in terrestrial old world monkeys. The lateral surface of scapula was divided into two fossae by the spine which extended from the vertebral border to its neck (Fig. 1).
Preuschoft et al. (2010) stated that the shape of the scapula of primates suited to provide its resistance against compression, and the scapular spine further afforded the enormous bending strength to it. The ratio of supraspinous to infraspinous fossa was approximately 1:2 as in horse (Sisson, 1953) but in contrast to dog (Miller, 1949) and ox (Raghavan, 1964) it was 1:1 and 1:3 respectively. In the arboreal monkeys, apes and in some strepsirhines, the scapula showed an elongated and wide infraspinous fossa (Preuschoft et al., 2010). The nutrient foramen was present almost in the middle of the infraspinous fossa in monkey (Fig. 1) in contrast to dog it was present on the distal 4th of medial surface (Miller, 1949). The height of spine close to the vertebral border, in the middle and in its distal end was 25, 10.5 and 15 mm respectively. The free edge of spine was thick and rough and showed variation in thickness as near vertebral border it was 3.35 mm, in middle 1.39 mm and at the distal end it was 2.08 mm, but in dog it was thick at origin and thin towards the neck (Miller, 1949). The spine was directed cranioventrally. It became more prominent distally and ended to a pointed projection of acromion process (Fig. 1). The acromion process was elongated (26 mm in length), thick, directed caudomedially and extended beyond the glenoid cavity. In contrast to dog, it was limited opposite to the rim of the glenoid cavity (Sisson, 1953). A prominent acromion process in terrestrial monkeys has also been reported by Preuschoft et al. (2010). The distance between rim of the glenoid cavity and distal end of acromion process was 75 mm.
On the costal surface the subscapular fossa was deeply concave in its length and had two separate rough triangular areas, the facies serrata (Fig. 2). The cranial borders was strongly convex and rough dorsally, concaves and smooth ventrally (Fig. 2).
It was thin at proximal end (1.23 mm), became thicker (1.38 mm) in the middle and thickest (2.02 mm) at the distal end. According to Fischer (1994), the length of cranial part of scapula served as a long lever for the foreswing of limb and reduced the force necessary to keep the scapula in place and was long enough to offer bony insertion to many muscles in the terrestrial old world monkeys. The caudal border was almost straight and thin (2.66 mm) in its proximal part, it soon became wide in form of a groove enclosed by two straight ridges (Fig. 3). The groove was thickest (9.33 mm) in middle and became thin (7.78 mm) at the distal end.
Vertebral border was strongly convex and thin (1.79 mm) at the cranial angle, thick (2.14 mm) in the middle and thickest (3.49 mm) near the caudal angle (Fig. 2). It was pitted due to impressions of cartilage. The cranial angle of scapula was rounded off and the caudal angle was acute in rhesus monkey. Preuschoft et al. (2010) also reported acute caudal angle in more arboreal monkeys, as well as in the apes. The glenoid angle joined the body of scapula at neck which was 21.82 mm in thickness. The glenoid cavity was very shallow and elongated oval in outline (Fig. 4). Its length and width measured 16.5 and 11 mm respectively. Preuschoft et al. (2010) also reported a narrow and elongated glenoid cavity in terrestrial monkeys. This was in perfect agreement with functional necessities of the respective forms, especially the frequent elevation and abduction of the arms in conditions that implied high loads. Tuber scapulae was present infront of glenoid cavity (Fig. 4). A long pointed well developed hook like coracoids process was present along its medial side (Fig. 4). A coracoids process has been reported to be absent in dog Sisson (1953). However, Miller (1949) stated that the coracoid process was like a small tubercle in dog. According to Young (2006), the variability of scapular morphology in terrestrial monkeys is less recorded than arboreal forms.
It is concluded that in the scapula of Macaca mulatta the scapular spine with long acromion process, shallow elongated glenoid cavity and well developed coracoid process are certain adaptational modifications suited to their functionality and locomotion on ground and tree.