Humerus

“ The humerus presents a large convex oval head, on each side of which is a tuberosity for the implantation of the supra- and sub-scapular muscles: these tuberosities do not rise above the articular convexity, so as to restrict the movements of the shoulder-joint, as in the Horse and Ruminants, but exhibit a structure and disposition conformable to those which characterize the proximal extremity of the humerus in other mammalia which enjoy rotatory movements of the upper or fore-limb. ”

“ The tuberosities of the humerus form the convexity of the shoulder. When the arm is raised, the convexity disappears,—there is a slight depression in its place. The head of the bone can be felt by pressing the fingers high up in the axilla.
11. The humerus ends at the elbow in two bony prominences (internal and external condyles) . The internal is more prominent. We can always feel the olecranon. Between this bony projection of the ulna and the internal condyle is a deep depression along which runs the ulna nerve (commonly called the “funny” or “crazy” bone) . ”

“ The groove for the musculo-spiral nerve on the outer side of the humerus is over-arched at its upper part by a strong obtuse process; which is comparatively less developed in the Megatherium. The trochlear or inferior articular surface of the humerus presents, as in the Megatherium, two well-marked convexities, with an intervening concavity: this indication of the rotatory power of the fore-leg is confirmed by the form of the head of the radius. ”

“ We know that in man the displacements of the humerus which take place in the antero-posterior direction are known as movement or projection forwards, and movement or projection backwards, respectively. We do not say that the humerus is flexed or extended, because, in reality, on account of the position which the skeleton of the shoulder occupies, it is not able to flex or place itself on the line of prolongation of the scapula with which it articulates.
In quadrupeds it is not so. The humerus and the scapula are contained in almost the same vertical plane ”

“ The shaft of the humerus, protected as it is by heavy muscles, is not frequently fractured; and fractures of its less protected parts, as for example, the head, are complicated in such manner that resultant arthritis soon constitutes the more serious condition.
As a result of falls on frozen ground, kicks or any other form of heavy contusion, the humerus is occasionally broken. It is rarely fractured otherwise. Because of the force of contusions usually required to effect humeral fracture, the manner in which the bone is broken, with respect to direction, is variable. ”

“ The following observations are a proof of this: those persons who are weasel-armed (galiancones) from birth, owing to dislocation of the humerus, or when the accident has happened to them before they have attained their full growth, such persons have the bone of the arm shortened, but those of the fore-arm and hand are little inferior in size to the sound, for the reasons which have been stated, because the humerus is the bone nearest to the joint affected, and, on that account, it is shorter than natural ”

“ The species is at present represented only by a few fragments of the skeleton, but among these is a distal end of a right humerus, with the characteristic portions all preserved. The specimen agrees in its main features with the humerus of Meleagris gallopavo Linn., the most noticeable points of difference being the absence in the fossil species of the broad longitudinal ridge on the inner surface of the distal end, opposite the radial condyle, and the abrupt termination of the ulnar condyle at its outer, superior border. ”

“ The condyles of the humerus bear their normal relations to one another. The olecranon and the triceps tendon form a marked prominence on the back of the elbow, the tip of the olecranon lying above and behind the condyles. The lower end of the humerus lies in the flexure of the joint with the biceps tendon tightly stretched over it. The coronoid process is often broken, or the tendon of the brachialis torn. The median and ulnar nerves may be stretched or torn. Not infrequently the bones of the forearm are displaced towards the medial side as well as backward. ”

“ The humerus (b) is quite different from anything to be met with elsewhere in the Mammalia, being a short and very stout bone, rendered most irregular in its outline by the development of great crests and processes. It not only [Pg 369] articulates with the shoulder-blade, but has a separate surface for the reception of the extremity of the collar-bone (c) , which is a short bone resembling the vertebra of a fish. The shoulder-blade (d) is long and narrow, but stout and triangular in its form. ”

“ The relative length of the fore and hind extremities cannot be precisely determined from the present imperfect skeleton of the Scelidothere; but there is good evidence for believing, that the fore extremity was the shortest. The humerus is shorter than the femur by one-ninth part of the latter bone; and the radius, which wants only the distal epiphysis, must have been shorter than the humerus. Now the relative development of the fore and hind legs is one of the points to be taken into consideration in an attempt to determine the habits and nature of an extinct mammal. ”

“ In swallows, for example, the humerus is short, whereas the other arm bones are long, and the manus is unusually large and heavy. A short humerus gives better lever action in the flight stroke than a long humerus does. ”

“ If the tendency of the thigh bone to resemble a Mammalian type of femur (p. 100) is a fundamental, deep-seated character of the skeleton, it might be anticipated that a trace of Mammalian character would also be found in the humerus. For what the character is worth, the head of the humerus does show a closer approximation to a Monotreme Mammal than is seen in Birds, and is to some extent paralleled in those South African reptiles which approximate to Mammals most closely. ”

“ There is no collar-bone. The limb-bones have a distinct, though superficial, resemblance to those of hoofed animals; the humerus has no very prominent ridges for the attachment of muscles and no epicondylar foramen, and the femur no third trochanter. The fore-arm bones are separate, but are so articulated together and with the humerus as to give the fore foot no power of rotation. The manus in all existing wild species has five digits, though the pollex or first digit is very small, a mere dew-claw ”

“ A left humerus, of which the upper-third is wanting, and which is so much slenderer than the right as apparently to belong to a distinct individual; a left ulna, which, though complete, is pathologically deformed, the coronoid process being so much enlarged by bony growth, that flexure of the elbow beyond a right angle must have been impossible; the anterior fossa of the humerus for the reception of the coronoid process being also filled up with a similar bony growth. ”

“ Luxations of the humerus are but rarely followed by any serious accidents. Sometimes a swelling more or less considerable appears, immediately after the fall, in and around the arm-pit. This is the effect of an increased irritability of the part, and is seldom of long duration. Desault’s remedy for it was the application of compresses wet with vegeto-mineral water, or of cataplasms moistened with the same liquid. ”

“ The operation of external bodies, active, when they are thrown against the shoulder, passive, when the shoulder, or the arm, is forcibly driven against them, is always the cause of a fracture of the neck of the humerus. ”

“ The humerus is directed backwards, the fore-arm forwards, and the hand still more forwards. This angulation seems to facilitate movement, inasmuch as it is seen in even the Amphibia and the lower Reptiles, in which, however, the differences between the fore- and hind-limbs are less marked, indicating therefore a less specialised condition of the limbs. ”