DR. atJNTHEE ON THE ANATOMY OE HATTERIA. 
609 
Before I proceed to the next portion of the skeleton, I shall describe what I have 
noticed with regard to the muscles connected with this complex apparatus of ribs, in 
order to determine its probable function. 
After the skin and the latissimus dorsi (which, thinned into a cutis-muscle, descends 
to the middle of the side of the trunk) are removed, the series of the uncinate apophyses 
of the ribs are seen imbedded (fig. 33), and forming the boundary line between two large 
masses of muscles, the dorsal of which corresponds to the longissimus dorsi (including the 
sacro-lumbaris), the ventral to the obliquus externus. Their effects are antagonistic. 
The longissimus dorsi is divided by ligamenta intermuscularia (in number equal to the 
dorsal and lumbar vertebrae), each of them terminating at and attaching itself to the 
hinder edge of a rib and to the extremity of its apophysis. This division of the mass of 
this muscle renders it possible that certain portions of it can be called into action inde- 
pendently of the others. It raises the ribs, or part of them. Towards the middle of the 
back it is covered by a strong aponeurosis, from the median line of which arises a series 
of short, erect, conical muscles (fig. 33, b), each enclosed in an aponeurotic sheath, 
destined to move parts -or the whole of the dorsal crest. 
The ventral muscular mass forms a much thinner layer ; and although it can be divided 
into three strata, the whole must be regarded as M. obliquus externus , as all the fascicles 
run backwards and downwards (fig. 33, e). The outer stratum (<?') is fixed to the abdo- 
minal aponeurotic band ; and immediately below this line of attachment lies the hinder 
portion of the pectoralis major (d), which thus is received in a sheath, formed by a sepa- 
ration of the two outer strata of the obliquus externus. The innermost stratum is very 
thin, and frequently interrupted. The three strata coalesce as they approach the costal 
apophyses, the mass being divided into fifteen parts, each of which is inserted into the 
lower edge of a costal apophysis. The function of this muscle is to depress and draw 
backwards the ribs. 
Beside the inter costales, the outer stratum of which runs backwards and downwards, 
the inner having a backward and upward direction, irregular muscles, passing two or 
three ribs to insert themselves at the third and fourth, assist the function of the true 
intercostales ; they are found both on the inside and the outside of the ribs. 
Each of the dilated costal heemapophyses has two muscles : one (fig. 33, g) is flat, thin 
and broad, and arises from the concave anterior edge of its ventral portion, and is attached 
behind the insertion of the corresponding muscle of the preceding cartilage ; its fibres run 
obliquely forward and inward. The second muscle (Ji ) arises from the outer surface of 
the dorsal portion of the hsemapophysis, and is attached to the inner side of the joint 
between the next following cartilage and its rib ; its fibres run obliquely backward and 
outward. Sometimes a small fascicle is detached from this muscle, coalescing with the 
intercostalis of the same rib. I shall speak subsequently of the use of these muscles. 
On examining the ventral region of the trunk (fig. 32), we find that the cutis, which is so 
easily detached in other Saurians, is most intimately attached to a layer of strong fibrous 
tissue (c c ) extending over the entire lower surface of the abdomen to, and passing into. 
