10 II. W. MAUETT TIMS. 



an early ajL^e. In tlie .•^pcciiiu-u No. 24 the bizygomatic l>reailth measured G4 nun., the 

 liicraiiial tliatneter 1)ein,<,' Imt Gl mm. It is (hnilttful whether the rehitions of these two 

 diameters is of any importance, since in the two .skulls of Strnorr/ii/nchu.'^ Iq^onyx 

 measured l»y 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 

 lA'ptoni/c/iotis the widest part of the zygomatic arch is at its posterior end, the breadth 

 gradually diminishing as one pa.s.ses forwards. In this respect they agree with the adult 

 skull of Steiiorrhj/ncfitis, 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 (PI. II., fig. 12). The curvature involves the whole of the cervical and the 

 anterit)r jwrtion of the dorsal region. The bend is so consideraltle that the ventral 

 surfaces of the vertebrae are brought so close to the ventral body wall that the 

 trachea and a-sophagus are deflected to one side. Dr. Gadow made the suggestion 

 to mc that it might possibly l)e 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 

 eviilently caused by the actif)U 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 ea.sy to understand, 

 but apimrently 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 l»v the 

 mounted skeletons which are to be .seen in mu.seums.* 



Mttsailar si/stem. — So detailed and careful a description of the muscles and their 

 attachments in Otariit and Triclwchus having been given by Dr. Murie (9), it is 

 unnece.s,snry 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 cimsideration. 

 It is nece.s.sary, however, to repeat that the material was by no means in good 

 condition for di.ssection, the muscles Ijcing in a very brittle ccmdition, 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 imjiortance to the mu.scles as 

 Itcing of .systematic and phylogcnetic; importance. Bearing this in mind, I have 

 compared the mu.scles of the embryo .seal with the descriptions of the muscles of the 



• A inountcd, but not exhibited, Hkcleton of I'hoca vilulina in the Natural History Museum shows a 

 ncll-iuorkcil cun-aturo in the cervical region.— F. J. B. 



