386 THE ANIMAL KINGDOM. 



fused with the tibia, thus approximating to Aves. The Crocodile has a 

 well-developed calcaneal process. There is said to be an indication of a 

 sixth digit in Chelonia and Lacertilia. 



The cerebral hemispheres are smaller relatively to the rest of the brain, 

 and to the spinal cord than in Aves, and the Deinosaurian Stegosaurus 

 appears to have had a brain far smaller than the lumbar swelling in its 

 own spinal cord, and smallest relatively to the bulk of the body among 

 terrestrial Vertebrata. The olfactory lobes are well developed : the cerebral 

 hemispheres are largest in the Crocodilia and some Lacertilia, and have a 

 conspicuous corpus striatum. They are connected by an anterior com- 

 missure, and in the Crocodile there appears to be an indication of a fornix. 

 The thalami optici are usually hidden by the cerebral hemispheres and 

 optic lobes : the pineal gland is composed of non-nervous tissue and often 

 attached to the dura mater. The optic lobes are hollow and the optic tracts 

 often meet behind them dorsally. The cerebellum is either a mere trans- 

 verse lamella, or of fair size and folded on itself. There is generally a bend 

 between the medulla oblongata and the spinal cord. The ventricles of the 

 brain are large. The spinal accessory nerve is not differentiated in Ophidia, 

 and in most Reptilia the cervical sympathetic is double on both sides. 

 The nostrils lie usually at the apex of the snout, but just in front of the 

 orbits in Plesiosauria and Ichthyosauria, or near them in Ignanodon. Many 

 Lacertilia and the Ophidia have a nasal gland. The eyes are very small 

 in some Ophidia (Typhlopidae, Uropeltidae) and Typhline among Lacertilia. 

 In the Ophidia, the Geckoes, the Amphisbaenoidea, and some of the Scin- 

 coidea among Lacertilia, the eyelids are transparent and united together 

 forming a lacrymal chamber in front of the cornea. Other Scincoidea have the 

 lower lid partially transparent. The third lid is present in many Lacertilia, 

 in all Chelonia and the Crocodilia : and in the first-named is moved by a 

 bursalis muscle attached to the orbit ; but in the two other orders by a 

 pyramidalis springing from the back of the eyeball itself. The Ophidia 

 possess only the Harderian lacrymal gland. The sclerotic contains a ring 

 of bones in the Ichthyosauria, Chelonia and in many Lacertilia. There is a 

 pecten homologous with the similar structure seen in Aves in many Lacer- 

 tilia : traces of it are said to be found in many Ophidia and the Crocodilia, 

 but it is absent in Hatter ia among Lacertilia and in Chelonia, an order in 

 which the circular portion of the ciliary muscle only is developed. A 

 tympanic cavity is present except in Ophidia, Amphisbaenoidea and 

 Hatteria. There are three Eustachian tubes in the Crocodile. The 

 stapes is a rod-like bone, and when there is no tympanic cavity lies 

 among the muscles. The tympanic membrane is exposed except in some 

 Chelonia, the Ophidia, Hatteria and Chamaeleons, and is covered by a 

 moveable flap in Crocodilia. The cochlea has the commencement of a 

 spiral turn in Hatteria. 



