148 ON THE MORPHOLOGICAL CONSTITUTION OF 



it is an extention of this ossification which appears to form 

 the mastoidal limb, or attachment of the infra-ocular arch of 

 the maccaw. I shall, in the sequel, state the grounds on which 

 I regard as actinapophyseal all the bones developed in the 

 opercular membrane of the orbital of the bird. I regard the 

 lachrymal bone and the supra-orbital bone or bones of the 

 saurians, as referable to the same morphological category ; 

 and as due to arrangements in the fibrous operculum of the 

 orbit, similar to those in the bird ; as also the connection be- 

 tween the malar and the post-frontal of the crocodilian, as 

 well as the change in the direction of the jugal, and the 

 peculiar position of the squamosal in the typical lizards. 



The supra-orbital bone or cartilage, with the infra-ocular 

 bony arch, appears in various forms in the osseous fish ; and 

 the arrangements presented by this form of cranium clearly 

 indicate that these orbital bones are parts of a system of 

 actinapophyseal elements referable respectively to the eth- 

 moidal, pre- and post-sphenoidal, temporal, and occipital 

 sclerotomes, peculiarly modified and connected in front for 

 the protection of the orbit, and behind for the suspension of 

 the pectoral girdle. 



THE PRE-SPHENOIDAL SCLEROTOME. Its Centrum and 

 Neural Arch. It has been already stated that this sclerotome 

 is peculiar in the mammal, in the absence of its meta- 

 neurapophyses, while this mesial element is more or less fully 

 and largely developed in the other forms of Vertebrata. When 

 the cerebrum proper is developed, the sphenoido-frontal bone 

 is absent ; when the cerebrum proper is a mere film, as in 

 birds and reptiles, or is absent altogether, the sphenoido-frontal 

 is present. As the evidence on which this statement is based 

 is derived from the consideration of the varied relations of all 

 the primary elements in the different forms of cranium, I am 

 compelled, in this preliminary abstract, to refer those who are 

 desirous of weighing that evidence to what has been already 



