552 DR. J. MURIE ON THE ANATOMY OF THE SEA-LION. 
central tendon. They are each at first of considerable thickness, but not very broad, 
and, as they describe a semicircle backwards, narrow still further, and terminate almost 
linearly near the ligamenta arcuata. The central tendon with its divisions is compared 
in the human being to a trefoil leaf; here in the Sea-lion it assumes a form which 
might be likened rather to a pair of callipers. ‘The muscular fibres outside the tri- 
partite tendon have a radiate direction, those towards the sternum being directed 
forwards, those to the ribs and rib-cartilages forwards, outwards, or backwards, 
according as they are anteriorly, laterally, or posteriorly situated. 'The muscle inside 
the aforesaid tripartite tendon differs in the direction of its fibres. It forms two semi- 
lunes, whose concavities face each other and powerfully enclose the cesophagus: in a 
line behind this the pericardial fold is attached. ‘The left fleshy crus (/.c) is far more 
fully developed than is the right one. ‘There is no very clear definition of ligamentum 
arcuatum internum and externum, as in human anatomy, the loin-muscles entering the 
chest but meagrely. Instead, an arched or funnel-like fascia enclasps the aorta, fastens 
down the musculo-tendinous parts, and joins the fleshy constricted portion of the 
diaphragm, which ends in a tendon fastened to the bodies of the third and fourth 
lumbar vertebre (vide D, fig. 836, Pl. LX-XIII.). The opening for the vena cava (v.c) is 
situate between the central tendon and the right alar tendon. 
5. Muscles of the Loins and Tail. (Plate LX-XIII.) 
Psoas.—Al\though the Otary seems to have great power and mobility in the lumbar 
region, so far as wriggling movement is concerned, yet there is a certain weakness in 
the loins; for the flexibility of movement is in great part due to the great thickness of 
the intervertebral cartilages, and not to immense power in the psoas muscles, which 
latter, comparatively speaking, are weak and long. 
If insertion is taken as indicative of a certain muscle rather than the origin of the 
muscular belly, then the psoas magnus is not present in the Sea-lion; or at least what 
would correspond with the psoas magnus is so incorporated with what may represent 
the psoas minor (described below) that no separate description is needed. On the other 
hand, if origin and general appearance have most weight, the psoas parvus must be 
absent, and that here named the psoas parvus be the psoas magnus. 
It would appear contrary, then, to the general development of these psoas muscles, 
that in this case the psoas parvus is much the greater in bulk (fig. 36, Ps, Ps*). If 
such it is, the belly is long, and its terminal tendon rather short than otherwise. It 
arises by four long delicate tendons from the ventral surfaces and posterior ends of the 
first, second, third, and fourth lumbar vertebrae. ‘These origins are covered by the 
belly of the muscle, which extends outwards to the tips of the second, third, and fourth 
lumbar vertebree ; and the muscle, narrowing as it runs backwards, is inserted bya short, 
strong tendon into the prominence representing the ilio-pectineal eminence. 
The éliacus (11) is only of moderate bulk. It arises from the sides of the bodies of 
