684 MR FRANK J. COLE 



induced me to accept the existing nomenclature of the skeleton, i.e. that no revision 

 without the evidence of the vessels and nerves could have any permanent value. It is 

 clear, however, that a revision is necessary ; and, for example, the transversus oris may 

 possibly have to be broken up into three discrete muscles. 



1 am much indebted to the friendly interest of Baron A. Klinckowstrom, who has 

 been kind enough to present me with a number of excellent unpublished drawings of 

 Myxine. Due acknowledgment will be made when these are put to any use. I also 

 wish to express my indebtedness to the Government Grant Committee of the Royal 

 Society for a grant which has defrayed the expenses of this research. 



Perhaps I may repeat the statement made in my first Part, that although the present 

 work is purely anatomical, the morphology of the animal will be exhaustively considered 

 when the whole facts are available and have been co-ordinated. In conclusion, I feel 

 it is only right to refer here to the great assistance in preparing the key sections given 

 by Edinger's projection apparatus, as made by Leitz. Combined with a Zeiss A lens 

 the sections may be easily and quickly drawn with great accuracy. One may hope that 

 this apparatus will be sufficiently improved in the future to be available with higher 

 powers. 



2. Histology of the Muscles. (Fig. 7, a-e, numerals 1-5.) 



I do not propose in this section to enter into the histology of the muscles proper, 

 but simply to consider such microscopical details as have an anatomical bearing. A 

 transverse section of the parietal muscles reveals the fact, as recognised by Maurer, 

 that the muscle fibres are (at least) of two kinds, which are easily distinguishable even 

 with the low power of the microscope. There are other types of muscle fibre present 

 in Myxine, especially, as we should expect, in the tail, but these do not concern us here. 

 The two types mentioned above are the small plasmic " red " fibres, which physiologists 

 have shown to occur in rapid or strenuous muscles, and the large aplasmic "white"* 

 fibres which are found in sluggish or tonus muscles. Of the two, the red fibres are 

 much less numerous, but on account of their very rich vascular supply they are 

 strikingly picked out if the section has been stained with Mann's methyl-blue-eosin. 

 The red fibres are either absent or very sparsely scattered at the anterior end of the 

 parietalis, and also throughout the greater part of the caudal region, and elsewhere in 

 the thin ventral portion of the muscle. Apart from this, they may be said to characterise 

 the parietalis generally. 



The M. parietalis is formed by a number of dorso-ventrally compressed fasciculi, 

 which in transverse section appear as flattened sausage-shaped masses, arranged (more 

 or less) at right angles to the median vertical axis of the body. The greater part of 



* I use the terms " red " and " white " on account of their convenience, but I have not examined living material to 

 ascertain whether these fibres, as is often the case, actually are red and white in colour. Their rich vascularity at least 

 should give the plasmic fibres a reddish tinge in Myxine. Well-known examples of the two kinds of fibres are the 

 predominantly red fibres of the pectoral muscles of the pigeon and the white fibres of the similar muscles of the fowl. 



