OF COLYMBUS TOEQUATUS. 163 



A pair of musculotendinous slips arise by three separate digitations from near the 

 extremities of the fifth, sixth, and seventh vertebral ribs; these digitations converge, and pass 

 upwards and backwards to be inserted into the skin just over the apex of the scapula. 

 These muscles are apparently offsets from the serrati magni. 



Another pair of musculotendinous slips pass to the skin, from the muscles just external 

 to, and an inch below, the acetabula. 



Muscles of the Trunk. 



These need detain us but for a moment ; their arrangement is as usual exceedingly 

 complex, and probably presents no special peculiarities. It is only necessary, therefore, to 

 notice the general features of the muscles of this region. 



The head of the bird is large and heavy, and its neck comparatively long. From the 

 tip of the bill to the first rib, measures more than from the latter point to the end of the 

 coccyx. In flying, as well as in diving and swimming under water, this ponderous head 

 and neck are held straightly outstretched. To enable the bird to do this, and to execute 

 the varied and extensive, as well as exceedingly rapid movements of the head and neck 

 necessary to secure its living prey, the muscles acting upon these parts are well developed. 

 Their general disposition is as follows : — 



On the back the opisthotenar muscles commence about opposite the crests of the ilia, 

 and extend along the fossae on each side of the spinous processes of the vertebra?. But 

 as there is very slight mobility of this portion of the spine, the muscles are comparatively 

 small and flat, and are moreover tendinous for a considerable portion of their extent. 



On the back of the neck, just anterior to the shoulders, where the greatest strain from 

 the weight of the head and neck is experienced, the aggregate bulk of the muscles is ex- 

 ceedingly extensive, much greater than at any other point along the spine. They are also 

 almost wholly carneous, each of the numerous slips being muscular rather than tendinous, 

 almost from their very origin. This is the point where the greatest mobility is required, 

 as well as the greatest strength ; and the two indications are fulfilled by the preponder- 

 ance of the contractile over the non-contractile portions of the muscles, together with the 

 increase in actual bulk of the muscular tissues. 



Passing along the neck toward the head the bulk of the muscles decreases, and they 

 become more tendinous, to the middle, but from this point toward the head their size and 

 fleshiness again increase, until near the occiput the aggregate volume of the complexus, 

 trachelo-mastoideus, &c, amounts to nearly as large a mass as is found at the root of the 

 neck. This is necessary for the adequate support of the large and heavy head. 



Biventer ceroids. The pair of muscles thus homologized by comparative anatomists, and 

 which exists so constantly throughout the class, is very distinct in this species. Through- 

 out their whole extent they receive no slips, and have no accessory attachments. They 

 arise from the spines of the lowest cervical, or anterior dorsal vertebra?, as two slender 

 round fleshy bellies ; their central tendons are two or three inches long, after which the 

 muscles again become fleshy, and as such are inserted side by side into the superior ex- 

 tremity of the occipital spine. The muscular portion thus considerably exceeds the ten- 

 dinous. 



The other individual muscles of the neck do not require special mention in this connec- 

 tion. 



MBMOIES BOST. 60C. SAT. HIST. Vol. I. Pt. 2. 42 



