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Parker's alisphenoid bone is thus, as I find it, even in 55 mm specimens, simply a part of the 

 ascending process of the parasphenoid, and I am unable to explain how Parker could have found it, 

 separate and independent, not only in a 2 inch (50 mm) but also in a 4 inch (100 mm) specimen. 

 Parker furthermore states that his alisphenoid is an endosteal bone. In my 55 mm and 80 mm 

 embryos the corresponding basipterygoid process of the parasphenoid is, in its anterior portion, 

 surrounded by dense tissue the character and origin of which I am unable to determine, not being 

 suffieiently versed in the subject; but it would seem to result, in part, from the breaking down of the 

 superficial layers of the cartilage against which the bone lies. In the 19 mm and 25 mm specimens this 

 dense tissue is already being developed, but at these ages the tissue lies almost entirely between the 

 bone and the cartilage, and it may accordingly be wholly of perichondrial origin. Whatever its origin, 

 this part of the parasphenoid certainly has relations to the underlying cartilage somewhat different 

 from those of the other portions of the bone, and it would seem to be a typical case of a dermal bone 

 in process of acquiring primary relations to an underlying cartilage. It is, however, to be noted 

 that perichondrial bone has nowhere eise appeared, in the earliest of the stages examined, and that 

 when it does appear it is not imbedded in dense formative tissues, as the bone here in question is. 

 In the adult this part of the ascending process of the parasphenoid certainly has much the appearance 

 of perichondrial bone; but it runs insensibly into the posterior portion of the process, where both 

 plates of the V-shaped portion of the bone are certainly of ectosteal origin, for they both extend 

 beyond the dorso-lateral edge of the cartilage they enclose, and there overlap, superficially, portions 

 of the inner and outer surfaces of the ventro-mesial edge of the proötic bone. But, whatever its 

 origin, this part of the parasphenoid is certainly not the alisphenoid, for that bone is found elsewhere, 

 in its proper place, as a wholly independent ossification. 



In the adult, on the anterior edge of the basipterygoid portion of the ascending process of the 

 parasphenoid, there is a tit-like process which projects toward and sometimes even abuts firmly 

 against the lateral surface of the body of the parasphenoid slightly anterior to the base of its ascending 

 process. This little process lies in a horizontal position, at right angles to the axis of the parasphenoid, 

 and between it and the anterior edge of the basal portion of the ascending process there is a more 

 or less completely closed opening which transmits the efferent pseudobranchial artery. The anterior 

 edge of the tit-like process is straight and forms part of the articular surface for the metapterygoid, 

 the remainder of that articular surface being formed by the straight anterior edge of the basipterygoid 

 process and a corresponding edge of that part of the proötic cartilage that lies dorso-lateral to the 

 process. This little tit-like process is thus a mesial growth of the anterior end of the V-shaped part 

 of the bone of embryos, and it is to be remarked that, although it may abut firmly against the body 

 of the parasphenoid, I have never found it fused with that bone. It is not shown in any of Parker's 

 figures, but the general arrangement of the parts can be readily understood by reference to those figures. 



Between the proötic bone and the hind edge of the externa! plate of the ascending process 

 of the parasphenoid, there is an opening which leads into a short canal between the parasphenoid 

 and the overlying cartilage of the basis cranii, the opening thus having exactly the position of the 

 internal carotid foramen of Amia and teleosts, and unquestionably being the homologue of that 

 foramen. In Lepidosteus, however, this foramen transmits the common carotid, which artery, 

 immediately within the foramen, separates into its external and internal branches. The external 

 carotid, turning upward, traverses a foramen that perforates the ventro-mesial edge of the proötic, 

 but lies partly in that bone and partly in the cartilage that bounds it. The artery then runs upward 



Zoologica. Heft 57. 24 



