20 EVERS'S COMPARATIVE ANATOMY. 



anchylosed, and the body and cornua of the os hyoides are fully 

 developed. 



In the anterior extremity, which is attached to the inner side of 

 the chest, we distinguish scapula and clavicle united by suture ; 

 humerus twisted, with a large articular condyle; radius and ulna 

 short, strong, and expanded inferiorly, fixed in a state of pronation; 

 carpal bones, sometimes as many as ten, arranged in three rows; 

 five short metacarpal bones; and the phalanges, two for the thumb 

 and last finger, and three for each of the others. 



The ilia are long and cylindrical in the land tortoise ; the pubis 

 and ischium broad and flat. The femur presents indications of 

 trochanters, as in man ; its head is large, and joins the shaft at a 

 right angle. There is no round ligament in the hip, though rudi- 

 ments of semilunar cartilages connected to crucial ligaments in the 

 knee. The tibia and fibula are separate. The metacarpal bones 

 are five, and the number and arrangement of the phalanges the 

 same as observed in the phalanges of the fingers, with the exception 

 of the outer toe, which is generally rudimentary. In the aquatic 

 chelonia, the bones of the extremities are longer, straighter, and 

 more slender than in the land species. 



Ophidia. — The skeleton in serpents consists of little more than a 

 vertebral column, possessing such a degree of mobility as enables 

 them to creep with speed along the surface, to swim through the 

 waters, to spring into the air, to climb trees, and to combat with and 

 conquer their prey. Extremities are here wholly absent, and the 

 spinal column and ribs constitute the sole organs of progressive 

 motion. For this reason the spine is characterised by immense 

 strength and great mobility. The vertebrae are more numerous 

 in this than in any other class of animals, being 49 in the anguis 

 fragilis, or blind worm ; 201 in the crotalus horrid us, or rattle-snake ; 

 and 316 in the coluber natrix. The bodies of the vertebrae have 

 ball and socket articulations, so disposed as to admit of free lateral, 

 but limited antero-posterior motion. The ribs of serpents are tubu- 

 lar, narrow and compressed from before backwards. Their head 

 presents a broad, arched, concave surface, to articulate with the 

 rounded, prominent, transverse processes of the vertebra?, whilst 

 their ventral extremity tapers to end in a thin, flexible cartilage. 

 The ribs extend from the atlas to the anus, and are 32 pairs in the 

 blind worm, 175 in the rattle-snake, and 204 in the coluber natrix. 

 They are all of the false kind, there being no rudiment of sternum, 

 except in the ophisaurus and blind worm alone, in which also faint 

 traces of shoulder and pelvis may be discerned. 



The head resembles the preceding order (or that of the chelonia) 

 in the small size of the cranium, whilst the multiplicity and detached 

 condition of its bones ally it to the fishy tribes. This loose state of 

 the component elements of the head is necessary in serpents, for, 

 being deprived of organs of prehension, they are compelled to swallow 

 their prey entire. As a consequence of the looseness of the other 

 bones, the two parietals are anchylosed along the median line, to 



