172 LECTURE Yin. 



and developes and supports ganglionic masses, principally disposed 

 in a linear series parallel with the axis : this part is called the ' brain' 

 or encephalon : the rest of the axis I term the ' myelon ' * ; retaining 

 its columnar or chord-character, and, being lodged in the canal of 

 the spinal column, it is usually defined as the medulla spinalis, spinal 

 marrow, or spinal chord, i 



In the Lamprey the myelon is flattened, opaline, ductile, and 

 elastic, as in the Lancelet and other Dermoptei-i : in typical Fishes 

 it is inelastic and opaque, cylindrical or sub-depressed, of nearly 

 uniform diameter, gradually tapering in the caudal region to a point 

 in heterocercal Fishes, but swelling again into a small terminal 

 ganglion f in most homocercal Fishes. 



The Hunterian preparation of the skate {Raia Batis, No. 1347.) 

 shows a slight (brachial or pectoral) enlargement of the myelon 

 where the numerous large nerves are sent off to the great jsectoral 

 fins I : a feebler brachial enlargement may be noticed in the Sharks. 

 I have not recognised it in osseous Fishes ; not even in those with 

 enormous pectorals adapted for flight, e. g. Exoccetus and Dacty- 

 lojiterus : in the latter the small ganglionic risings upon the dorsal 

 columns of the cervical region of the myelon receive nerves of sen- 

 sation from the free soft rays of the pectorals, and the homologous 

 ganglions are more marked in other Gurnards ( Triglce), which have 

 from three to five and sometimes six pairs, e. g. in Trigla Adriatica. § 

 Similar myelonal cervical ganglions are present, also, in Poly- 

 nemus. In the heterocercal Sturgeon there is a feeble expansion of 

 the myelon at the beginning of the caudal region, whence it is con- 

 tinued, gradually diminishing to a point along the neural canal in 

 the upper lobe of the tail. In some bony fishes (Trout, Blenny), the 

 caudal ganglion is not quite terminal, and is less marked than in the 

 Cod or Bream, in which it is of a hard texture, but receives the last 



* Gr. juusAos, marrow. As an apology for proposing a name, capable of being 

 inflected adjectively, for a most important part of the body which has hitherto 

 received none, I may observe that, so long as the brief definitions, ' marrow of the 

 spine,' ' cliord of the spine,' are substituted for a proper name, all propositions re- 

 specting it must continue to be periphrastic, e. g. 'diseases of the spinal marrow,' 

 ' functions of the spinal chord,' instead of ' myelonal diseases,' ' myelonal functions : ' 

 or, if the pathologist speaks of ' spinal disease,' meaning disease of tlie spinal marrow, 

 he is liable to be misunderstood as referring to disease of the spinal or vertebral 

 column. But, were the Anatomist to speak of the canal in the spinal marrow of 

 Fishes as the ' myelonal canal,' he would at once distinguish it from the canal of 

 the spinal column. The genei-ally accepted term ' chorda,' or 'chorda dorsalis,' for 

 the embryonic gelatinous basis of the spine, adds another source of confusion likely 

 to arise from the use of the term ' spinal chord,' applied to the myelon, or albu- 

 minous contents of tlie spinal canal. 



t Mil. p 6. ; Liv. p. 26. (in the Cod). 



\ This structure is accurately figured by Mr. Swan in liv. pi. xi. 



§ LV. pi. 2. fig. 4. p. 106. ; and Liii. p. 6., pi. 2. fig. 24, 25. 



