The diaphragm in man : a record of our present knowledge of its development, relationships, structure, and mode of action / by J.F. Halls Dally.

  • Dally, John Frederick Halls, 1877-1944.
Date:
[1908?]
Catalogue details

Licence: In copyright

Credit: The diaphragm in man : a record of our present knowledge of its development, relationships, structure, and mode of action / by J.F. Halls Dally. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    African toad (^Xenopas) (^■‘). This dorsal inuscnlar sheet pro- bably represents only the spinal segment of the diaphragm, as has been shown by Keith ^yho has minutely reinvestigated the anatomy of these toads, and has pointed out that the amphibian diaphragm is composed of three parts—a spinal portion derived from the anterior or cervical part of the trans- versalis sheet, a ventral part from the fourth segment of the rectus sheet, and a central part from the cervical amphibian aponeurosis referred to above. These tail-less forms [Xenopus, Pipa) “liave certainly been derived from long-tailed amphibians, and, on the suppo.sition that the mammalia have also been evolved from a primitive amphibian form (stego-cephalia), it is probable that the same elements which gave rise to the diaphragm in Anura may also have become modified to form a corresponding structure in mammals (^-). B.—Morphological Muscular Kelationships. The primary system of musculature, of which the structure of the leech is an example, consists of a single muscular plane from endoderm to ectoderm. The most complicated muscular arrangements gradually have been evolved from this simple Jfcype merely by successive segmentations which change the direction of the muscle-fibres. As the late Professor G. M. Humphry pointed out, the imperfect segmentation and individualisation of the muscles of Urodela to some degree affords a natural method of determining the relations which the muscles of the higher animals bear to one another and of grouping them, the segmentation. into planes being merely the result of the varia- tion in direction of fibres at different depths. The salient morphological relationships of the diaphragm I have tried to indicate in the accompanying Table I., where we see the trunk- musculature separated by the intervention of the primitive vertebral axis into two main dorsal and ventral groups which are homologous with similar dorso- and ventro-lateral groups of the broad lateral muscle of fishes and tailed amphibians. Those of the dorsal group become spinal muscles; the ventral set are still further subdivided into ventro-mesial and ventro- lateral divisions. In all but the lowest vertebrates, whilst the mesial group of ventral muscles retains the longitudinal direc- tion of its fibres, and is the least altered, the lateral portion of the ventral muscular sheet is divided into three chief planes. In the ventro-mesial set the rectus laver, although lost over the thorax, is prolonged into the neck as the anterior flat muscular