Dept.] NATURAL SCIENCES OF PHILADELPHIA. 5 



cle running in various directions, the result of their actions being to diminish 

 in all directions the calibre of the organ. The muscles first alluded to had 

 their attached ends towards the caudal extremity of the fish, and ran nearly- 

 parallel with the axis of the body : their length, not including the tendons, 

 was about ^ inch, or less. 



Under the microscope, fully-formed striated muscular fibre was observed in 

 these structures. The fibres measured about l-1350th of an inch in diameter, 

 and the ultimate fibrillar were very coarse. In the heart, the muscular fibres 

 measured about l-1200th of an inch, but their ultimate fibrillar were much 

 more delicate. 



Dr. Packard was at some loss to recognize the use of this peculiar structural 

 arrangement. Dr. Hammond had examined many fishes, but had never met 

 with striated muscular fibre in this organ. Dr. Mitchell thought that the great 

 rigidity of the scaly covering on this fish might render necessary some addi- 

 tional means of contracting the air sac. He thought the question as to how it 

 was filled a more difficult one. The gar can have no suctorial power, and the 

 air sac is surmounted by a glottis admirably calculated to exclude the air. 

 Dr. Hammond called attention to the degenerated state of the muscular tis 

 sues of this specimen. They were more or less converted into fatty matter, 

 and this was especially the case in the muscles of the belly. 



Dr. Mitchell described the peculiarities of the circulatory apparatus of 

 the gar pike. In this fish a hepatic vein and a vein from the muscles 

 of the left side open at the same point into the auricle ; a third vein from the 

 muscles of the right side opens into the auricle by a separate orifice. The mouths 

 of all these veins are provided with more or less perfect valves, whose edges 

 are attached to the walls of the auricle by tendinous cords and muscular 

 columns. The auricle is very large and easily dilated. The auriculo-ventri- 

 cular opening has a short fringe-like valve which extends around two thirds of 

 the aperture. The ventricle is small, and very thick. In the specimen exam- 

 ined, no distinct valves could be seen at the orifice through which the ventricle 

 delivers its blood into the bulbus arteriosus, nor were there any valves such as 

 are usually found in the arterial bulb itself. The interior of this organ was 

 furnished with six rows of projecting wart-like prominences, each of which 

 was connected with the one above and the one below, in the same row, by deli- 

 cate and nunieroiis tendinous filaments whose office it was difficult to compre- 

 hend. 



II. Physiology. 



1. Dr. Mitchell drew the attention of the Department to a peculiar contraction 

 which is produced when a blow is struck over any of the muscles which are not 

 very firmly bound down by fascia. 



Dr. Stokes of Dublin, long ago observed that when he percussed the skin 

 over the pectoralis muscle, its fibres contracted responsive to the stimulus 

 of the blow. While percussing certain consumptive patients, Dr. Mitchell noticed 

 that as the bar of muscle ceased to contract, a second contraction took place 

 nearly at right angles to the first one. By it the skin was raised into a promi- 

 nence, some lines in breadth and rather longer than the space covered by the 

 percussing finger end. This secondary contraction so slowly disappeared that 

 it seemed to be due rather to the action of organic non-striated muscle, than 

 to the striated variety of which voluntary muscles are composed, and which is 

 habitually rapid in its mode of contraction and of relaxation. Further observa- 

 tion showed Dr. Mitchell that a large part of the muscles, which are neither 

 deeply, placed or firmly bound down by fascia, are able to exhibit both ot the 

 forms of contraction here alluded to. Thus the extensor muscles of the leg and arm 

 are not very susceptible to this form of direct stimulus, while the flexors and most 

 of the muscles of the trunk, both before and behind, can be made to exhibit 

 both forms of contraction by tapping them smartly and quickly with the finger 



1859.] 



