640 MR. c. H. o'donoghue on the 



IV. Two longer ciliary branches (Aa. ciliares posticfe longfe, 

 Kathke), one of which runs forward on the inner side of the eye 

 and the other outward on its hinder side. 



V. A Retinal Artery (Art. centraHs retinae, Rathke) which 

 enters the eyeball with the optic nerve and spreads out over the 

 retina. 



(B) Veins. 



The veins of the head of Tropidonotus natrix have recently 

 been described in great detail by Bruner (13), who also describes 

 a muscular mechanism in the head whereby the blood-pressvire in 

 it i veins and sinuses may be considerably increased. It is not 

 possible by ordinaiy dissection to make out all the small vessels 

 given by that author, and, as my own results agree closely with' 

 his, it will only be necessarvj for the sake of completeness, to give 

 a brief description of the cephalic veins. 



The Mandibular Vein (V. inf ram axillaris, Schlemm ; Y. mandi- 

 bularis, Bi'uner) arises from a small sinus at the anterior end of 

 the lower jaw and runs backwards close to and on the outer side of 

 the external carotid artery. On its way it receives veins from the 

 trachea, tongue-sheath, muscles of the floor of the mouth, and . 

 the pharynx. It runs into the maxillary vein immediately before 

 the latter joins with the lateral cephalic vein to form the common 

 jugular vein. The bases of the mandibular, maxillary, and lateral 

 cephalic veins and the anterior end of the coinmon jugular vein 

 are surrounded by constrictor muscles whose morphology and 

 function are described by Bruner (loo. cit.). 



The Maxillary Vein (V. palatina, Schlemm ; V. maxillaris, 

 Bruner) also commences in a small sinus which is situated just 

 behind the premaxilla. This sinus has a double anastomosis with 

 the similar one on the other side. From this point it runs back- 

 wards beneath the naSal cavity along the floor of the orbit and 

 then above the palate to join the mandibular vein at the angle of 

 the lower jaw. During its course it receives : — 



I. The Rostral Vein (Y. rostralis, Bruner), which enters at the 

 level of the anterior anastomosis and brings the blood from a 

 venous network at the front end of the snout. It also receives 

 nasal veins (Y. nasales esternse, dorsalis, and ventralis, Bruner) 

 from the nasal gland. 



II. The Suhnasal Veiii (Sinus subnasalis, Bruner), which enters 

 at the level of the posterior anastomosis. It drains a somewhat 

 complex system of subnasal sinuses, which a,nastomose with one 

 another at the posterior end of the nasal cavity and which receive 

 also the palato-pterygoid vein. 



The Palato-pterygoid Vein (Sinus palato-pterygoid eus, Bruner) 

 runs from near the anterior to near the posterior end of 

 the skull on the inner side of the palatine and pterygoid 

 bones, and flows into the anastomosis between the sub- 

 nasal sinuses. 



