854 published articles
The right and left cricothyroid may cross the midline and interdigitate before inserting onto the cricoid cartilage. A very small band of muscle may be found on the inferior lateral aspect of the thyroid cartilage. It does not have any association with the cricoid, hence its function in this location is difficult to understand. It has, however, the elegant name of incisurae mediae obliquus (Gruber), and it may be found unilaterally or bilaterally.
This variant may be found arising from the anterior aspect of the cricoid arch and inserting on the posterior aspect of the hyoid body. Gruber also describes a cricohyoideus medianus . The cricohyoid has been considered a variant of thyrohyoid.
An occasional band of muscle may be found in contact with the lower border of the posterior cricoarytenoid. The ceratocricoideus (of Merkle) (or keratocricoid) is a short muscle arising near the lower border of cricoid cartilage, a little behind the inferior cornu of the thyroid cartilage, and passing obliquely outward and upward to be inserted into the inferior cornu of the thyroid cartilage. This variation was found in seven of 32 (21.9%) bodies studied and it usually exists on one side of the body only. According to Hetherington, the incidence of this variation is actually about 17%.
In females, this muscle is represented by a few fasciculi on the round ligament. It may arise, in part from the transversus abdominis. The muscle may arise from two different sources, transversus abdominis and internal oblique muscles. Reference Anson, B.J., Ed. (1966) Morris' Human Anatomy, 12th Ed., The Blakiston Division, McGraw-Hill Book Company, New York. Williams, P.L., Warwick, R., Dyson, M. and L.H. Bannister, Eds. (1989) Gray's Anatomy, 37th ed. Churchill Livingstone, Edinburgh.
This muscle varies in its differentiation and extent and may be fused with other muscles in the region. The absence of the orbital part of corrugator has been reported. See also orbicularis oculi. Syn.: Corrugator muscle, Coiter's muscle. Reference Anson, B.J., Ed. (1966) Morris' Human Anatomy, 12th Ed., The Blakiston Division, McGraw-Hill Book Company, New York.
This muscle is chiefly a flexor muscle, although in the arm it corresponds to the adductor mass seen in the thigh. It develops from a tissue mass that forms biceps and brachialis and is supplied by the musculocutaneus nerve. The muscle actually consists of three parts: (a) a proximal part arising from the coracoid process and inserted onto the humerus close to the lesser tubercle; (b) a middle part of intermediate size; and (c) a distal part, which is the largest and most superficially placed.
Because a considerable degree of independence may exist between the bundles of fibers coming from different areas of the line of origin, this muscle has been described as consisting of various parts designated pterygopharyngeus, buccopharyngeus, mylopharyngeus, and glossopharyngeus. Frequently, a bundle of fibers arises from the basilar portion of the occipital bone, or even from the inferior surface of the petrous portion of the temporal bone or the spine of the sphenoid, and passes downward to be inserted along with palatopharyngeus.
The portions of this muscle arising from each of the two laryngeal cartilages may be more or less distinct and have been named thyropharyngeus and cricopharyngeus. The inferior constrictor may be more or less united with fibers from cricothyroid, sternothyroid, and thyrohyoid. A slip ( syndesmopharyngeus ) from the lateral thyrohyoid ligament frequently occurs.
The coccygeal muscle varies greatly in the extent of its fleshy development. It may be doubled or partially fused with levator ani. Occasionally it is absent. M. curvator coccygeus accessorius or sacrococcygeus anterior arises from the lower anterior part of the transverse process of the fourth sacral vertebra and inserts onto the edge of the third and fourth coccygeal vertebra. Reference Gruber, W. (1887) Ein seltener Curvator coccygeus accessorius beim Menschen, homolog dem constanten Depressor caudae longus bei gewissen Säugethieren. Arch. Path. Anat. Physiol. Klin. Med. 109:1-4.
This muscle is variable in structure judging from the descriptions given by various authors. Peikert, Platzek, Besséde and May studied the relationship between the bulbospongiosus muscle and the external anal sphincter. They reported that the perineum contains several fascial layers composed of elastic and collagen fiber including bundles of smooth muscle fibers. The bulbospongiosus was found subdivided into a ventral and dorsal portion, which developed into four variants.
Brachioradialis is often united with brachialis at its origin, and its origin may extend proximally as far as the insertion of deltoideus, with which it may be connected. It may also be joined to extensor carpi radialis longus and abductor pollicis longus. The muscle may be divided, with the second belly attached distally to the radius (near the tuberosity), or even the ulna. In about 7% of cases, the tendon is split into two or three slips, occasionally allowing the radial nerve to pass through and by doing so becomes a potential entrapment site for the nerve.
The most frequent varieties of the muscle consist of its subdivision into two or more parts. When the muscle is divided, the distal insertions are irregular and variable. The parts may be attached to the coronoid process of the ulna, radius on or below the tuberosity, radius and ulna, radius and a tendinous band between it and the coronoid process, fascia of the forearm (the part or slip is then named brachiofascialis of Wood), or muscles of the forearm arising from the medial epicondyle.
The two parts of biceps femoris probably represent two separate muscles that are united in humans. In rare cases, the parts remain separate either partially or entirely or the short head may be absent. The two parts are innervated by two different nerves. The normal attachment of the muscle to the crural fascia represents an extension to the leg that is found in some mammals. The crural extension may be seen as muscular slips (tensor fasciae suralis) attached to the fascia, gastrocnemius, or tendo achillis.
This muscle is very variable. In about 12% of arms, a humeral head is found in addition to those usually found arising from the coracoid process (medial or short head) and the glenoid lip of the scapula (lateral or long head). A biceps with more than two heads is found in about 8% of Chinese, 10% of white Europeans, 12% of Black Africans, and about 18% of Japanese. A biceps may be composed of 1 to 5 heads. In one small study of 18 subjects, an accessory head was found six times, and a fourth head was found once.
In about 4% of cases studied, axiobasilaris (also atlantobasilaris internus [Gruber]), extends along the medial border of longus capitis from the anterior tubercle of the axis (or atlas) to the base of the skull. See mm. Longus capitis and longus colli.
The common variety of axillary arch is a fleshy slip of varying dimensions, often divided by a tendinous intersection, which extends from latissimus dorsi, through the axillary fascia, to pectoralis major, or to the short head of biceps brachii, or to the coracoid process of the scapula. Slips arising from digitations of serratus anterior on ribs 6 and 7 and joining pectoralis minor or coracobrachialis have also been described as axillary arch muscles. Axillary arch muscles were discovered by Ramsay in 1795.
It is uncommon for the ear muscles to be absent; the most frequently absent, however, is the anterior. Auricularis may join the styloglossus muscle. Syn.: m. epicranius auricularis anterior, epicranius temporalis, attrahens auriculare (Albin). References Austoni,A. (1908) Muscoli auricolari estrinseci dell'uomo. Arch. Ital. Anat. Embriol. 7:193-243. Bertelli, D. (1890) Le muscle auriculaire anterior. Arch. Ital. Biol. 13:354. Reid, R.W. and S. Taylor. (1879) Anatomical variations. Reports. St. Thomas's Hospital 9:44.
This muscle arises deep to vastus intermedius, from the distal third of the femur, and inserts into the fibrous portion of the articular capsule of the knee joint at the level of the suprapatellar bursa. See also Vastus intermedius , for additional information on this muscle. Reference Didio, L.J.A., Zappala, A., Cardoso, A.D., R.A. Diaz. (1969) Musculus articularis genu in human fetuses, newborn and young individuals. Anat. Anz. 124:121-132. Macalister, A.
The scalenes vary in the degree of their costal and vertebral attachments, as well as their interrelationship caused by the fusion of numerous fascicles. A problem of definition has been compounded by the authors who ascribe various muscles to different parts of the scalene muscle mass. Frequently (about 30% of cases studied) a poorly defined muscle mass is present. A scalenus minimus (intermedius (Testut), pleuralis [LeDouble]) may originate from the anterior tubercle of the sixth and seventh cervical vertebrae and inserts on the first rib (behind the subclavian groove).
Anconeus may be united, in varying degrees, with triceps, extensor carpi ulnaris, or epitrochleoanconeus (if present). It may represent a portion of the triceps that has been segmented off in this position. Frequently referred to as the fourth head of triceps, this muscle may also be absent. The muscle may also be represented by a fibrous band. See also triceps brachii. Syn.: m. anconeus quartus, anconeus parvus, Knorrenmuskel.
