Velayudham Spear in hand of Karthikeya is Brain and Spinal Cord

Karthikeya is depicted in puranas as son of Siva, who emerged from Agni and was raised by 6 mothers.
First instance of Kartikeya can be found in Yajurveda, Taitteriya Aranyaka 10.1.15
रुद्रो रुद्रश्च दन्तिश्च नन्दिः षण्मुख एव च । गरुडो ब्रह्मा विष्णुश्च नारसिहंस्तथैव च ।।
rudro rudrascha dantischa nandi sanmukha eva cha | garudo brahma vishnuscha narsimhastathaiva cha ||
Devas mentioned in this hymn are Rudra, Danti, Nandi, Shanmukha, Garuda, Brahma, Vishnu, Narsimha.
Karthikeya Velayudham Brain Spinalcord

Here Sanmukha (6 faced) is Kartikeya or Kumara Swamy, who was later appointed as commander-in-chief of Devas.
Atharva Veda describes him as ‘Agnibhuh‘, means a form of fire or evolved from fire.
Satapatha Brahmana refers to him as the son of Rudra and the six faces of Rudra. The Taittiriya Aranyaka contains the Gayatri mantra for Shanmukha. The Chandogya Upanishad refers to Skanda as the “way that leads to wisdom”. Upanishads also make a reference to a Supreme Being called Guha, the indweller. In tamil his names are Murugan, Kumara, Senthil (red one), Guhan, Armugam. He is refered as , which means God of Tamil.
Puranas such as Skanda, Siva, Kartika and also itihasas like Ramayana, Mahabharata have mentioned Kartikeya in multiple legends like killing Tarakasura (Surapadma), marrying valli and devasena.
Gods described in puranas are actually cosmic allegories and Kartikeya is one such force.
His weapon is a spear, called Sakthi or Vel.
This Velayudham in reality is our brain and spinal cord or rather Skull and Backbone around them.
Kartikeya holds Vel is his hand, which means that he controls the nervous system which is connected to brain and spinal cord.
In Vedic (Hindu) Astrology, Aries (Mesha) rasi is the head of Kala Purusha and Scorpio (Vrischika) is Anus.
Kalapurusha - human anatomy
Back bone ends right above anus, where mooladhara chakra is placed.
Both aries and scorpio signs are ruled by Mars, which is Fire (Agni) planet and controlled by Kartikeya.
That is how he holds a spear (Sakti/Vel) which denotes Brain till end of backbone.

The earliest coinage of Karthikeya found are from Yaudheyas period (300-200 BCE). Later, Kushan ruler Huvishka minted more coins of Karthikeya in 1st century CE.
Karthikeya coins Yaudheyas

Kartikeya is Sarpa (Kundalini)

Karthikeya Kundalini Spinalcord
In few puranic and local legends, he is described to have taken form of a Sarpa (snake) and travelled to many places.
In many South Indian temples, Kartikeya is also called as Subrahmanya, i.e सु (su) meaning “good” and ब्रह्मन् (brahman) meaning “transcendent reality, eternal truth” and worshipped in form of a Sarpa (snake).
This sarpa form is actually Kundalini energy which resides in our Mooladhara Chakra.
Kundalini is in sleep mode. Only when Mooladhara is activated, the elephant energy (Ganapati) pushes it upwards and kundalini travels towards brain to reach Sahasraha Chakra.
To activate mooladhara, ganapati mantras are to be applied. That is why the tradition of starting any event or pooja with Ganapati pooja has begun.
This removes the obstacles (Vighna) caused by our balance karma, which are residing in mooladhara (root-cause). That is why Ganapati is called Vighna-Nayaka or Vinayaka.
Kundalini crawls upwards like a sarpa (english word Serpent derived from it).
To represent this activated energy, Subrahmanya or Kartikeya is worshipped in form of Snake.

Sarpa Doshas in Horoscope

Sarpa Dosha
Sperm is in serpent shape and also crawls in same manner.
Sarpa Dosha or Naga Dosha does not mean just killing snakes or reptiles.
Even killing a unborn child (abortion) will have same effect as sperm is considered similar to snake (its shape and crawling method).
The concept of Manglik (Kuja dosha) is fake as it actually applies only to children below 16 years and that too with regards to their health.
In practial world, Sarpa or Naga dosha is main reason behind lack of next generation.
Kartikeya controls Mars (Mangal) which in turn is the cause behind them.

Krittika Nakshatra – 6 Mothers of Karthikeya

The puranic story of 6 mothers is clearly described in Mahabharata, Shalya parva, Chapter 44.

In days of yore the vital seed of Maheshvara coming out, fell into a blazing fire. The consumer of everything, the adorable Agni, could not burn that indestructible seed. On the other hand, the bearer of sacrificial libations, in consequence of that seed, became possessed of great energy and splendour. He could not bear within himself that, seed of mighty energy. At the command of Brahman, the lord Agni, approaching (the river) Ganga, threw into her that divine seed possessed of the effulgence of the Sun. Ganga also, unable to hold it, cast it on the beautiful breast of Himavat that is worshipped by the celestials. Thereupon Agni’s son began to grow there, overwhelming all the worlds by his energy. Meanwhile (the six) Krittikas beheld that child of fiery splendour. Seeing that puissant lord, that high-souled son of Agni, lying on a clump of heath, all the six Krittikas, who were desirous of a son, cried aloud, saying, “This child is mine, this child is mine!” Understanding the state of mind of those six mothers, the adorable lord Skanda had breastmilk from all having assumed six mouths.

Karthikeya Krittika Nakshatra Pleiades
In reality, Kritiika Nakshatra (Pleiades), which starts at end of Mesha Rasi is actually seen as a cluster of 7 stars (1 Kartikeya and 6 mothers).
The six Krittikas who raised the Hindu God Kartikeya are Śiva, Sambhūti, Prīti, Sannati, Anasūya and Kṣamā.
In Greek mythology, the Pleiads were the seven daughters of Atlas, a Titan who held up the sky, and the oceanid Pleione, protectress of sailing. The sisters were Maia, Electra, Alcyone, Taygete, Asterope, Celaeno and Merope.
In Hindu Astrology, Krittika and Visakha are called Misra nakshatras, which are favourable for activities like worshiping, fire ceremonies, purchasing furniture and electronics.
Other name of Kartikeya is Visakha, as Krittika starts in Aries (Mesha) and Visakha ends in Scorpio (Vrischika), which form Skull till end of backbone.
Visakhapatnam city is formed on this name and it used to have a Lord Visakheswara temple on beach, which was drowned and is predicted to emerge in future.
visakheswara temple

Kartikeya killing Tarakasura or Surapadma

Tarakasura or Surapadma is described in puranas as son of Vajranga and his wife Vajrangini.
In reality, he is EGO or Arrogance. Taraka means that which enlightens or evolves. Taraka-asura is the anti of that enlightenment.
Karthikeya Peacock Cock
When human ego reaches a state where mind thinks ‘I have conquered and mastered everything, I know everything.‘, this state of mind is denoted by Tarakasura.
To destroy such false pride, ego and arrogance is the job of Kundalini, who is Kartikeya.
Puranic story goes that Taraka (ego) after being defeated by Karthikeya assumed the form of a chicken or a rooster. A chicken is a symbol of weakness, lack of steadiness, and lack of patience. Generally if someone is a coward they say, “You are a chicken“.
Tarakasura (Ego) became a chicken or rooster and Peacock after being defeated by Karthikeya.
After losing battle, Taraka prayed to always be at the feet of the Lord. This means that ego should always be kept subdued. So Karthikeya made him the emblem on His flag. Ego is necessary in life but it should be kept subdued. That is how Kartikeya got name of Kukkuta Dhwaja (Hen Flag/Symbol).
Peacock denotes fickle mind. It never stays constantly at one place. When mind is fickle, it cannot concentrate and meditate on Paramatma.
Peacock is shown as his vehicle, which means that he mastered the Mind and kept under control.
Only we control fickle mind and subdues Ego, we become eligible to meditate upon kundalini.
Karthikeya Peacock Cock

Significance of Karthikeya marriage with Valli and Devasena

Karthikeya Valli Devasena
Karthikeya is also said to have married 2 women, Valli and Devasena.
There are few local fake stories about Valli being a tribal girl and Devasena being daughter of Indra.
When Murugan is not human, how can he marry a tribal girl ?
Valli means ‘Creeper‘. Spinal Cord is a tube-like structure which consists of bundles of nerve fibers. These nerve fibers appear like creepers.
Devasena : Kartikeya was appointed as commander-in-chief of devas army to kill Tarakasura. So he became leader of deva-sena (army of devas). Krittika nakshatra described above is Karthikeya, which is considered leader of gods.
Valli : He is actually the Kundalini controlling force in our bodies. The Velayudham he holds is our backbone through which kundalini has to crawl upwards like a serpant and its tip is our skull, where it has to open up the Sahasrara (crown) chakra). Valli means to crawl or creep. Creeper plants are called Valli or Lata (creeper of vine).
Kundalini is a Sanskrit word meaning either “coiled up” or “coiling like a snake.
six chakras body
His 6 faces (Shan-Mukha) are 6 chakras which he passes through before reaching crown.
That is why he controls serpants and serpant eating peacock is his vehicle.
Activating Muruga in your Mind will open up the Ajna Chakra (3rd eye of Siva), which will eventually increase consciousness and transcends to a higher realm.