236 



The hind-limb consists of femur (thigh bone), fused tibia 

 and fibula (lower leg), tarsus (ankle) composed of four 

 tarsals, and foot with five complete digits, each having a 

 metatarsal and from two to four phalanges. The two 

 proximal tarsals (inner astragalus and outer calcaneum or 

 os calcis) are greatly elongated. On the inner side of the 

 preaxial hallux or first toe, there is an extra digit, the 

 calcar. 



Describe (1) the Brain and Nerves, and (2) the Sympathetic 

 Nervous System of the Frog. 



(1) For principal parts of brain, see page 201. Only the 

 stalk of the pineal body is present. There is an optic chiasma. 

 The cerebellum is a narrow transverse band. The roof of 

 the medulla has a choroid plexus. The ten cranial nerves 

 are as in Scyllium, and their general distribution is similar. 

 The ganglia of the roots of nerves V. and VII. together 

 form the Gasserian ganglion. The first pair of spinal nerves 

 are absent in the adult ; each nerve of the second pair 

 gives off a hypoglossal to the tongue (the twelfth cranial 

 in higher Craniates), and also unites with the third to form 

 the brachial plexus of the arm. The sciatic plexus of the 

 leg is formed by the union of spinal nerves VII. to X. 

 Round the ganglia of the dorsal roots of the spinal nerves 

 there are sacs (see endolymphatic duct, page 206) containing 

 calcareous otolithic particles. 



(2) Along each side of the dorsal aorta there is a cord or 

 chain of ten pigmented sympathetic ganglia, each cord is con- 

 nected anteriorly with the Gasserian ganglion. See p age 202. 



Write a Short Account of the Alimentary System of the Frog. 



The buccal cavity (see page 233) opens into a short and 

 wide gullet or oesophagus, which leads into the stomach. 

 At the end of the stomach is the pyloric constriction. The 

 duodenum (first portion of small intestine) is parallel with 

 the stomach. The small intestine is a long narrow coiled 

 tube. The large intestine (rectum) is short and wide, and 

 it opens into the cloaca. The liver has two main lobes, 

 and the left one is subdivided into two ; between the main 

 lobes is the associated round gall-bladder. Short ducts from 

 liver and gall-bladder join to form the long bile-duct ; it 

 traverses the pancreas (situated between stomach and 

 duodenum) and, receiving the pancreatic duct, becomes the 

 common duct of liver and pancreas, entering the duodenum 

 about half an inch from the pylorus. 



