10 H. W. MARETT TIMS. 
an early age. In the specimen No. 24 the bizygomatic breadth measured 64 mm., the 
bicranial diameter being but 61 mm. It is doubtful whether the relations of these two 
diameters is of any importance, since in the two skulls of Stenorrhynchus leptonyx 
measured by Turner, the bizygomatic was greater in one, the bicranial in the other. 
A point to which it is possible greater importance may be attached is that in the foetal 
Leptonychotes the widest part of the zygomatic arch is at its posterior end, the breadth 
gradually diminishing as one passes forwards. In this respect they agree with the adult 
skull of Stenorrhynchus, but differ from that of the adult Weddell’s Seal, in which the 
widest part is at the mid-point of the arch. The most interesting point which I have 
observed is the extraordinary downward curve in the cervical region of the vertebral 
column (Pl. IL, fig. 12). The curvature involves the whole of the cervical and the 
anterior portion of the dorsal region. The bend is so considerable that the ventral 
surfaces of the vertebre are brought so close to the ventral body wall that the 
trachea and cesophagus are deflected to one side. Dr. Gadow made the suggestion 
to me that it might possibly be a sexual character present only in the males and 
caused by the habit of lifting the females when pairing. I therefore made median 
sections of both sexes and found that the curvature is a constant feature, and further, 
that it tends to become accentuated with the increasing age of the foetus. It is 
evidently caused by the action of the powerful muscles on the dorsum of the neck 
which, by approximating the head to the mid-dorsal region, have caused a “ buckling-up ” 
of the spinal column while in a cartilaginous and plastic condition. The particular 
mechanical advantage to be derived by this condition is not quite easy to understand, 
but apparently a.short stunted neck is of value to aquatic animals as evidenced by 
the Cetacea and Sirenia. In these mammals the shortening is brought about by an 
antero-posterior compression and a partial fusion of the individual vertebral centra. 
In the seals, however, the same end has been attained by different means. I am not 
aware of this fact having been noticed before; it certainly is not shown by the 
mounted skeletons which are to be seen in museums.* 
Muscular system.—So detailed and careful a description of the muscles and their 
attachments in Otaria and Trichechus having been given by Dr. Murie (9), it is 
unnecessary for me to do more than note the points in which the muscles of these 
animals appear to differ from those of the foetal specimens under consideration. 
It is necessary, however, to repeat that the material was by no means in good 
condition for dissection, the muscles being in a very brittle condition, so that, 
in spite of care, the facts here recorded must be taken with a certain amount of 
reservation. 
Writers on mammalian myology attach considerable importance to the muscles as 
being of systematic and phylogenetic importance. Bearing this in mind, I have 
compared the muscles of the embryo seal with the descriptions of the muscles of the 
* A mounted, but not exhibited, skeleton of Phoca vitulina in the Natural History Museum shows a 
well-marked curvature in the cervical region.—F. J. B. 
