Studies on the Vertebrate Head: Part I. Fish

Abstract

ABSTRACT In a paper of this nature it is difficult to epitomize the results any more briefly than has been done in the actual text. Only a few of the more important conclusions will be summarized. The vena capitis medialis is the primitive head vein. It is replaced by the vena capitis lateralis by different methods in the different groups.The relations of the efferent pseudobranchial artery to the trabecula cranii differ in Selachians and the remaining Craniates. This may be explained by vessel-looping in the Selachian or by the different relations of the polar cartilage.The relations of the hyomandibular to the veins, hyomandibular muscle, and facial nerve in the different groups suggest that the hyomandibular (i) of Selachians is a true hyomandibular, (ii) of Teleosts and Amia a compound of an interarcual cartilage and a processus oticus hyomandibularis, the latter being a modified extra-hyal.The schematic condition of the true hyomandibular with the processus oticus hyomandibularis is shadowed in Ceratodus, embryonic stages.A certain number of constant relations exist, as set forth on p. 328.