THE VASCULAR SYSTEM 223 



but one rather large vein, which may be termed the F. orbito-nasalis 

 (v.o.na.) leaves the anterior end of the plexus and passes postero- 

 mesially deep into the orbit to a point close to the optic fenestra, 

 where it receives the V. ophthalmica (v.oph.) from the bulbus oculi. 

 The ophthalmic vein passes inwards from the eye along the optic 

 peduncle. The V. orbito-nasalis then turns dorsalwards and dis- 

 charges into the posterior end of the peri-orbital network and more 

 particularly into the V. orhitalis superior^ (a factor of the V. petrosa 

 lateralis), and into the superior facial vein (a factor of the external 

 jugular). 



The V. orhitalis superior (v.o.s.) lies deep to, and drains, the M. 

 levator mandibulae anterior and the skin overlying it. It also drains 

 the deeper parts of the dorsal portion of the peri-orbital network as 

 already described. 



The V. orhitalis inferior (v.o.i.) is the ventral counterpart of the 

 above and drains the deeper regions of the peri-orbital network ven- 

 trally as well as a considerable portion of the levator bulbi muscle. 



Another important tributary of the V. petrosa lateralis is the V. 

 anastomotica (v.anas.) joining it to the palatal vessels. Sometimes it 

 joins the V. palatina itself, more frequently the maxillo-palatine vein, 

 and sometimes both vessels. 



The V. cranialis pro-otica (Gaupp, in Frog) (v.cr.pr-ot.) or V. cere- 

 bralis anterior (van Gelderen) is the chief vein draining the cranial 

 cavity. It leaves the skull together with N. ophthalmicus profundus 

 V and joins the V. petrosa lateralis mesially just as it enters the 

 antrum. 



Within the antrum a factor is received which enters the cavity 

 between the Proc. oticus and the Proc. ascendens; the V. petrosa 

 lateralis itself enters the antrum ventral to the Proc. ascendens, 

 between it and the Proc. basilaris. It drains the M. levator mandi- 

 bulae. Another small vein leaves the cranial cavity in company with 

 the Vllth nerve and joins the V. petrosa lateralis near the posterior 

 extremity of the antrum. It may be called the F. cranialis mesotica 

 (v.cr.m-ot.) and obviously corresponds with the V. cerebralis medialis 

 of van Gelderen. At about the same level a small factor draining the 

 loose connective tissue and skin immediately posterior to the ear can 

 usually be found. 



Van Gelderen has made a comparative study of the origin of the 

 veins draining the cranium in vertebrates, and it is apparent, from 

 his account, that the condition in Salamandra must be looked on as 

 primitive. 



(J?) Tht factors from the palate entering the F. pharyngo-palatina are 



