Ma^ 15, 1879] 



NATURE 



63 



adult lamprey, while other parts are as much specialised 

 as anything that can be found in the skull and face of a 

 man. There are no dermostoses, and no instance is known 

 in which a splint bone {paroslosis) unites with any part of 

 the ossified endocranium, except in the base of the skull, 

 where a rostrum of membranous origin unites with the 

 basisphenoid. The skull is largely formed of splint bones, 

 and the inner parts of the face are also formed of mem- 

 brane bones, which, however, represent cartilaginous 

 elements in fishes. The outer parts of the face are 

 formed of bones that have no cartilaginous representa- 

 tives in the lower forms, but exist as splint bones or 

 dermal scutes in the Ganoids, osseous fishes, and 

 Amphibia. So that in a mere study of the development 

 of the snake, without reference to other types, we should 

 find no difference between the premaxillaries and the 

 maxillaries on the one hand, and the palatines and the 

 pterygoids on the other. 



The whole apparatus of the palate and upper and 

 lower jaws is a very loosely articulated structure, and each 

 bone is kept as much as possible in the form of a simple 

 bar or splint. 



The hinder part of the endocranium and the auditory 

 capsules are intensely ossified, and contrary to what is 

 seen in any other vertebrata, the orbito- and ali- sphenoids 

 are separately developed in the membranous walls of the 

 skull ; they are both very small, especially the former. 

 The three bony elements of the auditory capsule remain 

 permanently separate, but the pro-otic unites with the 

 ali-sphenoid, the epi-otic with the supra-occipital, and the 

 opisthotic with the ex- occipital. 



The only visceral elements that are developed behind 

 the mandible are the rod of the columella and the minute 

 stylo-hyal which coalesces with the quadrate. 



Lizards. — The lizards form a very large group of 

 reptiles, all of which, like the snakes, have a movable 

 pier to the lower jaw, but which have a very remarkable 

 diversity of external and internal characters. Besides 

 the typical lizards, this order includes the AmphisbEenae, 

 the blind-worms, the chamasleons, and the New Zealand 

 Hatteria {Spfienodon). 



For practical zoology, all that can be seen and handled 

 in an animal without dissection is, of course, readiest and 

 best for classification, but to establish a sound foundation, 

 it is necessary to go much deeper. The brain, heart, and 

 other internal organs present very poor distinctive 

 characters in the families under consideration when com- 

 pared witn the skull, face, spine, and limbs. 



In the most serpentiform of lizards there' are at least 

 limb girdles even if there are no limbs. 



In several kinds, such as the Blind-worms {Anguisfra- 

 gilis) and the Australian Cyclodonts, there is a dermal 

 scute inside each horny scale. In the latter and also in 

 the Skinks {Mocoa), the underlying parietals and frontals 

 are extensively ankylosed to the overlying bony scutes. 

 In our native sand-lizards the investing bones that lie 

 next the skin, where there are no intervening muscular 

 fibres, become rough and thick, like ordinary dermal 

 scutes ; the horny skin over them is thin and has no 

 bony plates under it as in the body. In the larger 

 number of lizards, including the blind-worms, the three 

 normal ventral splint-bones— a pair and an odd one— are 

 seen ; in Hatteria these are continued along the abdomen 

 segmentally, as in the Plesiosaurs. These bones are sup- 

 pressed in the chamasleon, which deserves to represent a 

 sub-order by itself, so little has it conformed to the 

 normal type of the lizard. 



In the chamaeleon the outer bones of the head become 

 crested, scabrous, and fretted with all sorts of markings. 

 In such types as Monitor, Stellio, and Iguana, the cranial 

 roof-bones and the bones of the face are not rough, as in 

 the sand-lizard, nor fretted, as in the chameleon, but 

 smooth, as in the serpents and birds. 

 One of the most remarkable things in the skull of some 



of the types is the retention of rows of bones the counter- 

 parts of which must be sought for in the ancient Amphibia 

 of the Coal Measures and in the still more ancient 

 Ganoid fishes of the Old Red Sandstone. In the little 

 nimble lizard, for example, we have two rows of such 

 bones strengthening the eyebrows, and another row over 

 the temporal region, besides a bone flooring the outer 

 nostril, which belongs to the same category. 



A sort of anticipation of the hinge of the bird's upper 

 jaw is seen in the sand lizard and in the large stump- 

 tailed lizard of Australia (Trachydosaurus rugosus), in 

 which forms a fenestra appears in the orbito-nasal sep- 

 tum. This does not appear in the ostrich tribe, but 

 begins in the Tinamous. Considered evolutionally, this 

 is an exceedingly interesting and instructive fact. 



The parietals, which are simply roof-bones, are propped 

 up by a slender rod of bone, the so-called columella (epi- 

 pterygoid), which must not be confounded with the bone 

 of the same name in the middle ear. The chamseleons, 

 however, do not possess this bone, and they are also 

 deficient in respect of their ear, having neither the drum 

 and its parchment nor any rudiment of a cochlea. 



There is usually only one premaxillary, but in the 

 Skinks and Cyclodonts there are two. 



When the birds are spoken of as being genetically re- 

 lated to the lizards, it must be understood that modern 

 lizards are not referred to ; they are in many respects as 



J Mjy, J MU 



Fig. 3. — Diagram of chondrocranium of Lizard. ^ Letters as before, b.hy^ 

 basi-hyal ; co^ columella ; py^ pituitary spac*. 



much specialised as the birds themselves, and only form 

 a side branch, and not a leader of the vertebrate life-tree. 



Chelonia ^Turtles and Tortoises). — The extinction of 

 old, irregular, generalised tortoises has left their descend- 

 ants in a very neat and orderly state, showing a great 

 uniformity and distinctness from the other reptiles, in the 

 fact that the body is inclosed in a strong bony box 

 formed of the carapace and plastron. 



This box is formed of bony plates, covered with horny 

 scales, which, however, do not conform to them. The 

 inner skeleton in the walls and roof of this curious 

 building has become fused with the outer ; below there is 

 no inner skeleton, these animals having neither sternum 

 nor sternal ribs, the plastron and the marginal plates of 

 the carapace being formed by ossifications in the dermis. 

 The carapace is principally formed by the bony matter 

 from the spines of the back and of the rib-shafts spreading 

 into the thick overlying web of fibrous tissue. 



In some of the Mud Tortoises the edges of the cara- 

 pace are often soft, and the plastron is very imperfect. 

 In Chelydra and the Matamata the neck and tail are 

 much longer than usual, and remind the observer of the 

 Plesiosaurs. 



The plastron is formed of four bones on each side, the 

 anterior pair being separated by a single median piece,, 

 and thus only one of the median ventral bones of a 

 Plesiosaurus or Hatteria is retained. 



There are no teeth, the jaws being covered with horn, 

 and forming an efficient shearing apparatus. The facial 



