[11 J THE OSTEOLOGY OF AMI A CALVA. 757 



tensive fosssB are found on the skull, that extend well anteriorly to- 

 wards the frontal region (Fig. 1). 



As the dermal bones, occupying their respective places, the squa- 

 mosal and lateral margin of the parietal span this depression as the arch 

 of a bridge, it gives rise to a cavity between the primoidal cranium and 

 its cover-bone, the opening of which is upon the posterior aspect (Plate 

 II, Fig. 6, tg.^^) and into it enters, to be attached to the occiput on either 

 side, a part of the muscle of the dorsum of the trunk. 



This depression, which forms so striking a feature of the skulls in the 

 Teleostei, I here propose to name the temporal fossa.^^ 



Projecting from the middle line posteriorly there is a short cartilagi- 

 nous process (Fig. 3, Oc. ^^) that occupies precisely the same position 

 that the superoccipital does in the Teleostei. The last-mentioned bone 

 is wanting in the Siluroids and Dipnoi. From the hinder boundary of 

 the vault of the skull it is produced downwards and backwards, and 

 finally is drawn out as a cylindrical jjrolongation of the same, in which 

 is contained the posterior part of the medulla oblongata and the anterior 

 couimencement of tbe spinal cord. 



The occipital region ^^ of A7nia is, so far as a comparison with bony 

 fishes teaches us, remarkably drawn out longitudinally, and this pro- 

 longation, the cause and significance of which will be discussed further 

 on, concerns chiefly the region posterior to the foramen for the vagus. 



'8 This is given in the text of the original .as Th. and I here correct it to ig. — Trans. 



•9 This point is the proper one for us to take a careful look into the relations of the 

 squamosal to the primoidal cranium. This hone rests by its lateral border only upon 

 that crest of the primoidal skull which is directed upwards and outwards and forms 

 the lateral boundary of the temporal fossa. Now, although the squamosal in Amia, 

 as already stated, is a dermal bone, which appears only to be resting upon the pri- 

 moidal cranium, it would be impossible to remove it without injury. This is the site 

 it occupies: from the lateral margin of the bone are developed two osseous ridges, 

 which are directed downwards and to some extent towards the median line, and have, 

 when articulated, the two corresponding sharp cartilaginous crests of the skull in- 

 serted between them. The lateral ridge of the squamosal, of the two mentioned ones, 

 is juxtaopposed to the lateral surface of the skullj and is carried from the margin of 

 the bone downwards to the hyomandibular articulation. The remaining or mesial 

 ridge lies in the temporal fossa. This condition is significant in so far that among 

 the Teleostei it is only through the lateral margin of the squamosal, that the cartil- 

 ages are wedged apart, and the firm union of the bone with the primoidal cranium 

 takes place. 



20 This is Co. in the original text, and it has been corrected here to Oc. In either 

 event it is not quite clear what Dr. Sagemehl intends to indicate, so Oc. has been 

 omitted from my letters of reference, as I must believe he refers to 01. — Trans. 



*' It appears to me more to the point to consider the foramen for the glossopha- 

 ryngeal and the posterior border of the petrosal as the extreme anterior boundary of 

 the occipital region in the bony Ganoids and Teleostei, and not the foramen for the 

 vagus, as Gegenbaur has done for the Selachians. In the fishes examined by us these 

 two nerves are intimately related to each other, and in rare cases they may even have 

 a common foramen of exit, so that placing them in this or that region would be quite 

 arbitrary,. Moreover, in the limitation proposed by mo the confines of regions are 

 almost without exception defined by the sutures between the bones, and therefore it 

 becomes unnecessary to award a bone to different regions. 



