398 THE TISSUES. 



Distribution and Peculiar Forms of Striated Fibre in the Lower 



Animals. 



I. In the vertebrata, generally, the distribution of striated fibres 

 is as in man. The following peculiarities are noted : 



1. In the oesophagus (with smooth fibres), of some mammalia 

 and of the plagiostorne fishes ; around the contractile organ of the 

 pharynx of the carp ; and in the stomach of cobites fossilis, and the 

 intestine of tinea chrysitis, and around the anal glands and Cowper's 

 gland in mammals. 



2. In the skin of some mammalia, birds, serpents, and tailless 

 batrachians (frog, &c.), and the tactile hairs of mammals. 



3. In the lymph-hearts of many birds and amphibia ; and in the 

 right auriculo- ventricular valve, in birds, and the ornithorhynchus. 

 Also in the inferior vena cava of the seal, close above the dia- 

 phragm. 



4. In the interior of the eye in birds, and around the poison - 

 gland in serpents. 



The anastomosing fibres already mentioned, probably occur in 

 the hearts, and the lymph-hearts of all animals. Branched fibres 

 also occur in the tongue of all the vertebrata probably ; and are 

 found in the upper lip of the rat. 



II. In the invertebrata, all the muscular fibres belong genetically 

 to the striated form, whether they are clearly striated, or not. 

 (Kb'ttiker.Y' The muscles of insects, and of the medusae, and indeed 

 the heart, intestine, and muscles of the genital organs, of the inver- 

 tebrata generally, are distinctly striated. It is only necessary, 

 therefore, to notice the peculiar forms of striated fibre in this class, 

 which are enumerated by Kolliker. 



1. Muscular tubes, with homogeneous semi-solid non-striated 

 contents; i. e. the fibre is like the non-striated or smooth fibre, with 

 a distinct myolemma; as in most of the mollusca, annelidse, and 

 radiata. 



2. Tubes (myolemmata), containing a semifluid, homogeneous 

 layer in contact with them, and a fluid or granular central sub- 

 stance frequently transversely striated or nucleated ; as in Lumbri- 

 cidse, Hirudinidae, Carinaria, and Petromyzon and Paludina in 

 part. 



3. Similar tubes, having the cortical layer of their contents trans- 

 versely striated, but not divisible into distinct fibrillse ; as in many 

 muscles of the Hirudinidae. This form is found in the tongue, 

 pharynx, sphincter ani, &c., of fishes even. These tubes contain a 

 fluid in their centre. 



4. Tubes precisely like the preceding, except that they have no 

 central cavity (i. e. are demi-solid throughout), and break often into 

 disks, though not into fibrillae ; as in many Articulata (Salpce), and 

 some Radiata. 



