300 



ZOOLOGY 



SECT. 



directly inwards at its distal end, the manus being rotated so that 

 its pre-axial border looks inwards. 



The humerus is a long bone consisting of a shaft and two ex- 

 tremities, each of the latter being formed of an epiphysis of calcified 

 cartilage, the proximal rounded, the distal pulley-like (trochlea) with 

 two articular surfaces, one for the radius and the other for the ulna. 

 The radius is a slender bone consisting, like the humerus, of a shaft 

 and two epiphyses ; the distal extremity has a concave articular 

 surface for the carpus, and is produced pre-axially into a radial 

 styloid process. The proximal end of the ulna is produced into an 

 upwardly directed process the olecranon. The distal end bears a 

 convex articular surface for the carpus. The carpus (Fig. 909) is 

 composed of ten small polyhedral or rounded carpal bones. These 



consist of a proximal row containing 

 three, viz., the radiale (r), ulnarc (u), 

 and intermedium (i), of a ccntralc (c\ 

 and of a distal row of five (1-5) ; with 

 an accessory or^si/b?'m(f)bone attached 

 to the distal epiphysis of the ulna on 

 its post-axial side. The first digit or 

 polhx consists of a metacarpal and two 

 phalanges, the second of a metacarpal 

 and three phalanges, the third of a 

 metacarpal and four phalanges, the 

 fourth of a metacarpal and five phalanges, 

 and the fifth of a metacarpal and three 

 phalanges. The number of phalanges 

 in the first four digits is, therefore, one 

 more than the number of the digit. 



The pchic arch (Fig. 910) consists of 

 two triradiate bones, the ossa innominata, 

 each ray being a separate bone. On 



the outer side at the point from which the rays diverge is a concave 

 articular surface the acetabulum(Ac) for the head of the humerus. 

 From the region of the acetabulum one of the rays, the ilium (I), 

 a compressed rod, passes upwards and backwards to articulate with 

 the sacral region of the spinal column. A second ray the piibis 

 (P) passes downwards and forwards to meet its fellow in the 

 middle line, the articulation being termed the pubic symphysis. In 

 the middle in front, between the anterior ends of the pubes, is a 

 small nodule of calcified cartilage, the epi-pubis (Cep\ The third 

 ray or ischium (Is) runs downwards and backwards, and articulates 

 with its fellow in the ischiadic symphysis, the ventral ends of the 

 two bones being separated by a plate of calcified cartilage. Be- 

 tween the pubes and ischia is a wide space divided by a median 

 ligament (Ig) into a pair of apertures which are termed the obtu- 

 rator foramina. A small rod of bone, the os cloaca?, or hypo- 



r 



FIG. 909. Carpus of Lacerta 

 agrilis, (left) from above. R. 

 radius ; U. ulna ; c. centrale ; 

 i. intermedium ; r. radiale ; v.. 

 ulnare ; 1 5, the five distal 

 carpals ; t, pisiform ; IV, the 

 five metacarpals. (After Wieder- 

 sheim.) 



