COLYMBI 387 



divided into two about halfway down the neck ; the two 

 tracts are not again divided upon the trunk, where they are 

 broad. The spinal tract divides high up on the neck (Pocli- 

 ct'px crixhthis) or only between the shoulders (Columbus 

 glacialis). The anterior part of the spinal tract is stronger 

 than the posterior part, and is separated from it ; the latter is 

 solid, enclosing no space. 



The patagial tendons of Colymbus glacialis are rather 

 simple. The tendon of the brevis is a rather broad undivided 

 band. There is no patagial fan, but, as in ^Echmophorus, a 

 delicate tendon arises from the fore arm near the insertion of 

 the tensor brevis and ends in the biceps slip. In CoUjmbus 

 arcticus, according to FUBBRINGER'S sketch, a broad diffuse 

 tendon arises from biceps slip, and ends freely upon the 

 patagium. The first description given is from my own dis- 

 section of C. glacialis, and agrees with a manuscript note 

 of Mr. FORBES upon C. septentrionalis. But C. glacialis 

 apparently sometimes approaches C. arcticus. I have a manu- 

 script sketch by Professor GARROD showing a broad band of 

 fibres arising from the biceps slip, but ending on the fore arm. 



The anconceus has a humeral head. The expansor sccun- 

 (1 a riorum appears to be absent. The biceps is single-headed. 



The leg muscle formula, in contradistinction to what we 

 find in the grebes (where it is BX ), is ABX+ . 



There is a peculiarity in the gastrocnemius of C. septen- 

 trionalis which is worth calling attention to : one of the heads 

 of that muscle arises from the tendinous end of the glutens 

 maximus. 



The femorocaudal is tendinous for half its length ; its ac- 

 cessory is a very large muscle. The ambiens in Colymbus 

 glacialish&B two heads of origin. 



The combined plantar tendons give off a small slip to the 

 hallux in C. septentrionalis, as in Podicipes minor. 



The divers have two carotids, the more modified (cf. leg 

 formula) grebes only the left. 



The lobes of the liver in the Colymbi are equal, and there 

 is a gall bladder. 



The following are a few intestinal measurements :- 



c c 2 



