superior sagittal sinus 

 superior petrosal sinus 



occipital sinus 



postglenoid emissary vein 



inferior petrosal sinus 

 (dashed lii 



signnoid sinus 



/" I vii ^internal jugular 

 VII IX x.xi ^" 



A ORNITHORHYNCHUS B DIDELPHYS 



occipital arch 



FEUS 



TALPA 



Figure 11-34. Variations in venous drainage of mammals. (After von Gelderen, 1933) 



Bird The venous system of the bird is modified. Blood is 

 shunted below the middle-ear cavity in an external jugular 

 stem. The external jugular shunts of either side are inter- 

 connected, and the right jugular is the larger (turkey). 

 Drainage from the brain is by way of middle and posterior 

 cerebral channels and out through the foramen magnum as 

 well. 



The development of the venous channels can readily be 

 observed in the chicken. The 72-hour chick has a network 

 of channels above and below the nerve roots and the otic 

 capsule. The dorsal channel of the otic capsule has a divi- 

 sion passing lateral to the capsule. The 96-hour chick has a 

 single anterior cardinal channel which passes below the 

 vagus, lateral to the glossopharyngeal, below the otic cap- 

 sule, lateral to the facial, and below the trigeminal. This 

 channel has the same branches as the 10-mm pig. 



Amphibians In the salamander or frog, the pattern of 

 head veins is essentially that of the reptile. In the frog, there 

 is a small inferior jugular which extends to the musculature 

 of the throat; it has submental and shoulder branches. The 

 anterior cardinal stem also has large subclavian and bran- 

 chial divisions. This stem, as the vena capitis lateralis, ex- 

 tends into the head over the columella and through the 

 cranioquadrate passage; it enters the orbit above the trigem- 

 inal root. 



In the Bullfrog a posterior cerebral branch is lacking; the 

 middle cerebral branch of the lateral head vein enters the 

 skull and extends out on the dorsal surface of the optic lobes. 

 The vessels of either side converge on the posterior half of 

 the brain and are connected by a fine reticulum of vessels. 

 These vessels pass through the foramen magnum, side by 

 side, and back through the spinal canal on the dorsal sur- 

 face of the cord. 



The lateral head vein of the Bullfrog also receives an 

 orbital vessel which has branches extending out through 

 the ventral margin of the orbit along the maxilla anteriorly 

 and posteriorly. The posterior maxillary follows the course of 

 the maxillary artery to become the external mandibular 

 vein. There is also an internal maxillary division from this 

 orbital stem. The lateral head vein has a large palatine 

 branch which follows the palatine artery. 



In the salamander there is an inferior jugular passing 

 below the branchial region to the throat musculature. The 

 anterior cardinal (jugular) stem passes up behind the bran- 

 chial opening, or openings, and forward above these. At the 

 angle of the mandible, this stem receives several branches, 

 one from the outside of the mandible, another from the 

 maxilla. The main stem passes inward toward the jugular 

 foramen, through which the posterior cerebral branch pas- 

 ses, then forward through the cranioquadrate fissure as the 

 lateral head vein. 



364 



THE CIRCULATORY SYSTEM 



