AMPHIBIA 219 



lateralis system. In the adult it carries accessory fibres 

 to the muscles behind the head, and, running round the 

 oesophagus, divides into the laryngeal to the larynx, cardiac 

 to the heart, pulmonary to the lung, and the gastric to the 

 stomach. 



The spinal nerves also number ten pairs. They are : 

 I. hypoglossal, distributed to the muscles of the back and 

 shoulder, and running along the floor of the mouth supplies the 

 muscles of the floor of the mouth and tongue ; II and III form 

 the brachial plexus which supplies the muscles, skin, etc., of 

 the fore-limb ; IV, V, and VI supply the muscles and skin of 

 the body wall ; VII to X supply the nerves to the hinder part 

 of the body and the hind-limbs, and form the lumbar plexus. 



The sympathetic nervous system is plainly seen as a 

 pigmented series of ten ganglia connected by longitudinal 

 strands on each side of the dorsal aorta and in front thereof. 

 Each ganglion is connected with the corresponding spinal 

 nerve by a ramus communicans. The longitudinal nerve is 

 continued anteriorly to the ganglia of the cranial nerves 

 X, IX, and V. 



Sense Organs. The nasal cavity is resolved into a superior 

 and an inferior chamber, the one opening on the surface of the 

 head, and the other on the roof of the mouth. There is besides 

 a lateral chamber which opens at the junction between the 

 two cavities, and near it is the nasal opening of the lachrymal 

 duct. The nasal membrane is formed of long columnar cells 

 and sensory olfactory cells terminating in stiff processes. 



The nose originates as a thickening of the ectoderm on 

 each side, which becomes hollow and afterwards cup-shaped. 

 During the larval period & solid outgrowth of cells takes 

 place which extends to the endoderm of the roof of the mouth 

 and, becoming hollow, establishes the posterior naris. The 

 lachrymal duct arises also as a rod of cells from the ectoderm 

 intervening between the eye and the nasal cavity. 



The eye is covered by the conjunctiva, a transparent 

 membrane continuous with the ectoderm of the eyelids. The 

 sclerotic coat of connective tissue is chondrified internally and 

 it forms the eyeball. It is pierced by the optic nerve medi- 

 ally, and externally is transparent, forming the cornea. The 



