254 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 



by the (X.) vagus to reach the heart, lungs, &c. The (XI.) spinal 

 accessory, a nerve not present in the frog, is made up of fibres 

 arising from the side of the spinal cord and bulb, it leaves the 

 skull with the vagus, and supplies some of the neck-muscles. 

 The (XII.) hypoglossal nerve corresponds to the first spinal of the 

 frog, and has a similar distribution, but it arises from the ventral 

 surface of the bulb. 



For the nerve exits see p. 233. 



The spinal nerves arise by dorsal and ventral roots (the former 

 ganglionated) from the spinal cord, and pass transversely outwards 

 by the intervertebral foramina. They are named cervical, thoracic, 

 &c., in the corresponding vertebral regions. The brachial plexus, 

 from which the wing is supplied, is produced by the union of the 

 last three cervical with the first thoracic. A lumbar plexus is 

 formed by the last lumbar and first sacral nerves, and a sciatic 

 plexus by the five succeeding nerves. These two plexuses supply 

 the hind-limbs and their girdles. 



(3) Sympathetic System (Fig. 70, Sy). The main part of 

 this is a delicate ganglionated cord running close to the vertebral 

 column on each side. The ganglia are connected by rami com- 

 municantes with the commencements of the spinal nerves. The 

 two cords unite behind in an unpaired ganglion (ganglion impar), 

 while the anterior part of each of them is double, half of it run- 

 ning in the vertebrarterial canal. 



The same histological elements are present as in the frog, and 

 their structure and arrangement are similiar (cf. Fig. 61). There 

 are, however, no bipolar ganglia in the sympathetic of the peculiar 

 kind described on p. 215. The external part of the cerebellum 

 is composed of grey matter, its internal part and peduncles of 

 white matter. 



The most important advance upon the frog is found in the 

 large size of the cerebral hemispheres, and this is associated with 

 increased intelligence. The large cerebellum has apparently the 

 correlation of muscular movements for its main function. 



10. Sense Organs. (1) Tactile Organs. Many of the nerves 

 ramifying in the skin terminate in ovoid touch-corpuscles. 



(2) Gustatory Organs. Gustatory cells, supplied by the fibres 

 of the glossopharyngeal nerve, are present in the hinder part of 

 the tongue and roof of the mouth. 



