orbital sinus 

 superior orbital artery 



Harderian gland 

 nasal artery 

 nasal sinus 



temporal artery and vein 

 frontal vessels 



middle cerebral vein 

 internal maxillary 

 lateral head vein 



muscular ramus 

 occipital artery 

 columella ^poroccipital process 



posterior cerebral 

 stapedial artery 



XII 

 external carotid 

 1st branchial arch 



mandibular artery and vein 



internal mandibular 

 Figure 11-27. Vascular system of the head in Sphenodon. (After O'Donoghue, 1920) 



external maxillary arteries. The ophthalmic division emerges 

 with the optic nerve; it also serves the snout region of the 

 skull. 



The situation in Nectunu is not matched in the frog (Fig- 

 ure 11-28), although they agree in that the external carotid 

 forms only the lingual artery. The internal carotid passes 

 upward into the orbit, where it sends divisions upward, an- 

 teriorly, and into the cranial cavity. It serves the general 

 region of the eye, the ethmoid area, and part of the brain. 

 The supraorbital, maxillary, and mandibular divisions arise 

 from an artery passing forward over the top of the head from 

 the systemic stem. This artery also gives rise to branches pass- 

 ing into the skull and passing backward along the vertebral 

 column above and lateral to the spines of the vertebrae. 



In the frog or salamander, one observes a large swelling, 

 the carotid gland, at the base of the internal and external 

 carotids. This gland is derived from the gill and connective 

 vessel remnants between the first branchial afferent and ef- 

 ferent arteries; its function is not known, but its spongy na- 

 ture suggests control of blood pressure in the internal ca- 

 rotid. 



The arterial system of the frog is a modified one as deter- 

 mined on the basis of its embryological development. The 

 ontogeny of this region in the tetrapods shows many inter- 

 esting points. The three basic stems; stapedial, internal 

 carotid, and external carotid are probably primitive for the 

 mammal. In man a stapedial artery appears early but is 

 later replaced. The internal carotid and stapedials are de- 



rivatives of a common stem as suggested in the amphibian. 

 The external carotid is a lingual artery in the primitive type. 

 The modified type observed in the mammal is thus derivable 

 from the type observed in the salamander. Even in the case 

 of the salamander, there has been a certain amount of 

 alteration. The exact primitive pattern is not necessarily 

 repeated in any living form. 



Choanafe fishes There is no readily available figure or de- 

 scription of the head arteries for a choanate, but examina- 

 tion of Protopterus indicates that it is more like the fish than 

 the amphibian. The external carotid, as represented by the 

 hypobranchial branches of the hyoid efferent, serves the 

 hyoid arch and the throat area; it is a typical lingual artery. 

 The internal carotid is the dorsoanterior continuation of the 

 hyoid afferent; there is a broad dorsal connective between 

 the second and third arches. From the third arch an artery 

 extends forward through the palatoquadrate into the orbit; it 

 supplies the snout, maxilla, and mandible. 



Aclinopterygian fishes Two species of actinopterygians can 

 be compared in terms of their head arteries; these are 

 Ophiodon and Lampanyctus (Figure 11-29). Although these 

 two types differ greatly in detail, they agree in certain basic 

 features. There are four branchial arches in each. The ef- 

 ferent artery of the first branchial arch extends forward to 

 the hyoid arch as an external carotid; it follows the hyoid 

 arch back to the area of the interhyal, where it joins the 



CIRCULATION IN THE HEAD 



357 



