Archive image from page 259 of The cyclopædia of anatomy and. The cyclopædia of anatomy and physiology cyclopdiaofana0402todd Year: 1849 1044 THORAX. on the contrary, decrease in the degree of their obliquity as they proceed in the same direc- tion. Moreover, for the most part the ex- ternal fibres increase in their obliquity in the same intercostal space as you proceed from the vertebrae towards the sternum, and the internal intercostal fibres, on the contrary, increase their obliquity from the sternum towards the vertebra?, therefore they seldom decussate at right angles to each other, or
Archive image from page 259 of The cyclopædia of anatomy and. The cyclopædia of anatomy and physiology cyclopdiaofana0402todd Year: 1849 1044 THORAX. on the contrary, decrease in the degree of their obliquity as they proceed in the same direc- tion. Moreover, for the most part the ex- ternal fibres increase in their obliquity in the same intercostal space as you proceed from the vertebrae towards the sternum, and the internal intercostal fibres, on the contrary, increase their obliquity from the sternum towards the vertebra?, therefore they seldom decussate at right angles to each other, or form a perfect cross like the letter X. This is their general relative position at death, but, during life, in every stage of respiration, their degree of obliquity varies. The obliquity of the intercostal fibres should be viewed more with reference to the spine than to the ribs, because we shall show that their action is relative to the spine, and not to the ribs and that they may be perpendicular to two ribs, while they are oblique to the spine, because the ribs are themselves oblique. We have never seen any of the external intercostal fibres perpendicular to a rib, but we may see that arrangement in the internal layer of the lower intercostal spaces (fig. 673.). The omission of the relative posi- tion of the spine with reference to the ob- liquity of these muscles has led to many false conclusions as to their action in respiration. Let E E (Jig. 675.) represent a spine or a rigid Fig. 675. dicular to the two bars ; now move the bars up to p 3, also at an angle of 45° with E E, and the fibre L K becomes more oblique than at the position p 2. Therefore a tension may change from the oblique to the perpen- dicular relatively to the ribs; but it can never so change its relation to the spine. Thus L' K.' and i/ K' between the bars at P 3 cross each other, in the same direc~ tion, but in different degrees of obliquity; when the bars are at p 4., they decussate in directions c
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