261 



on 



eal 



two parts, one on either side, and the two resulting arteries turn forward 



dorsal to the basisphenoid bone, but completely enveloped in a dense 



layer of fibrous tissue that here covers the floor of the cranial cavity. 



Running forward in this tissue, each artery reaches the opticus perforation 



of the cranial wall, where it turns upward, leaves the membrane, and 



traverses a portion of the perforation itself, there lying postero-lateral 



to the issuing opticus. In this part of its course, where it appears, 



in sections, to lie wholly outside the cranial cavity, it gives oö" the 



retinalis artery, and then itself soon enters the dorsal or antero-dorsal 



edge of the membranous bounding wall of the opticus perforation ; thus 



again entering a space or canal in the side wall of the skull. It then 



soon perforates the mesial 



c er. a 



psb 



layers of the membrane 

 in which it lies, and there 

 first definitely enters the 

 cranial cavity. That the 

 artery has not properly 

 been inside the cranial 

 cavity up to this point, 

 is perhaps better shown 

 by the conditions in Be- 

 lone acus. In this fish, 

 a young adult of which 

 was also examined in 

 sections , the internal 

 carotid has a general 

 course strictly similar to 

 that in Scorpaena. But 

 as the artery, having 

 entered the preopticus 

 portion of the mem- 

 branous side wall of the 

 skull, turns inward to 

 definitely enter the cranial 



<^ 



amc 



aal 



ta 



aky 



Diagrammatic representation of the Carotid and 

 Related Arteries in Ameiurus. aal.. Afferent artery 

 of first branchial arch. ahy. afferent artery of hyoidean 

 arch. amd. afferent artery of mandibular arch, cer.a. 

 cerebralis artery, ea I. efferent artery of first branchial 

 arch. ehy. possible remnant of the efferent artery of 

 hyoidean arch. ec. external carotid artery, ic. in- 

 ternal carotid artery, on.a. orbito-nasal artery, psh. 

 so-called pseudobranch. ret. a. retinalis artery, ta. 

 truncus arteriosus. 



cavity as the cerebral artery, it gives ofi' a small branch. This small 

 branch continues forward a short distance in the side wall of the 

 skull and then pierces the external layers of the membranous wall and, 

 issuing on the external surface of the skull, goes to the eye ball, which 

 it pierces on its anterior surface. That the carotid should enter the 

 membranous side wall of the skull dorsal or dorso - anterior to the 

 opticus, and while still in the wall should send a branch to the ex- 



